/* ============================================
   TEXTBOOK SOLUTIONS LIBRARY — Premium SaaS
   Modern design, wired to the theme app shell
   ============================================ */

/* ═══════════════════════════════════════════
   DESIGN TOKENS (app-shell aware)
   ═══════════════════════════════════════════ */
:root {
  --tbs-primary: var(--qs-app-primary, #2563EB);
  --tbs-primary-hover: var(--qs-app-primary-dark, #1D4ED8);
  --tbs-primary-soft: var(--qs-app-primary-soft, #EFF6FF);
  --tbs-primary-border: var(--qs-app-primary-border, #BFDBFE);
  --tbs-primary-glow: color-mix(in srgb, var(--tbs-primary) 10%, transparent);
  --tbs-primary-ring: color-mix(in srgb, var(--tbs-primary) 18%, transparent);
  --tbs-secondary: #7C3AED;
  --tbs-bg: var(--qs-app-bg, #F8FAFC);
  --tbs-card: var(--qs-app-card, #FFFFFF);
  --tbs-card-soft: var(--qs-app-card-soft, #F8FAFC);
  --tbs-border: var(--qs-app-border, #E5E7EB);
  --tbs-border-light: var(--qs-app-card-soft, #F1F5F9);
  --tbs-text: var(--qs-app-text, #0F172A);
  --tbs-text-2: var(--qs-app-text-soft, #475569);
  --tbs-text-3: var(--qs-app-muted, #94A3B8);
  --tbs-success: #059669;
  --tbs-success-bg: #ECFDF5;
  --tbs-success-border: #A7F3D0;
  --tbs-warning: #D97706;
  --tbs-warning-bg: #FFFBEB;
  --tbs-warning-border: #FDE68A;
  --tbs-danger: #DC2626;
  --tbs-danger-bg: #FEF2F2;
  --tbs-r: var(--qs-app-radius, 18px);
  --tbs-r-sm: var(--qs-app-radius-sm, 12px);
  --tbs-r-lg: var(--qs-app-radius-lg, 22px);
  --tbs-r-xs: 8px;
  --tbs-r-pill: 9999px;
  --tbs-shadow: var(--qs-app-shadow, 0 1px 2px rgba(16,24,40,0.04), 0 1px 3px rgba(16,24,40,0.05));
  --tbs-shadow-sm: 0 1px 3px rgba(0,0,0,0.06);
  --tbs-shadow-md: var(--qs-app-shadow-md, 0 6px 16px -6px rgba(15,23,42,0.12));
  --tbs-shadow-lg: var(--qs-app-shadow-lg, 0 18px 40px -12px rgba(15,23,42,0.18));
  --tbs-shadow-xl: 0 24px 48px rgba(0,0,0,0.14);
  --tbs-shadow-glow: 0 0 0 4px var(--tbs-primary-glow);
  --tbs-ease: cubic-bezier(0.4,0,0.2,1);
  --tbs-sidebar-w: 250px;
  --tbs-right-w: 270px;
  --tbs-font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
}

/* Legacy dark toggle (theme uses html[data-theme="dark"] on the app shell) */
body.tbs-dark {
  --tbs-bg: #0F172A;
  --tbs-card: #1E293B;
  --tbs-card-soft: #0B1220;
  --tbs-border: #334155;
  --tbs-border-light: #1E293B;
  --tbs-text: #F1F5F9;
  --tbs-text-2: #94A3B8;
  --tbs-text-3: #64748B;
  --tbs-primary-soft: rgba(59,130,246,0.14);
  --tbs-primary-border: rgba(59,130,246,0.35);
  --tbs-success-bg: #052E16;
  --tbs-success-border: #064E3B;
  --tbs-warning-bg: #451A03;
  --tbs-warning-border: #92400E;
  --tbs-danger-bg: #450A0A;
  --tbs-shadow: 0 1px 2px rgba(0,0,0,0.35);
  --tbs-shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --tbs-shadow-md: 0 6px 16px -6px rgba(0,0,0,0.5);
  --tbs-shadow-lg: 0 18px 40px -12px rgba(0,0,0,0.6);
}

/* ═══════════════════════════════════════════
   RESET
   ═══════════════════════════════════════════ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
.tbs-wrap {
  font-family: var(--tbs-font);
  background: var(--tbs-bg);
  color: var(--tbs-text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  min-height: 100vh;
}
.tbs-wrap * { box-sizing: border-box; }
.tbs-wrap h1, .tbs-wrap h2, .tbs-wrap h3 { line-height: 1.25; font-weight: 700; letter-spacing: -0.02em; }
a { color: inherit; text-decoration: none; }

/* ═══════════════════════════════════════════
   HERO SECTION — glowing gradient + glass search
   ═══════════════════════════════════════════ */
.tbs-hero {
  text-align: center;
  padding: clamp(44px, 6vw, 72px) clamp(20px, 5vw, 40px) clamp(36px, 5vw, 56px);
  background: linear-gradient(135deg, #1E1B4B 0%, #4F46E5 55%, #7C3AED 100%);
  color: #fff;
  position: relative;
  overflow: hidden;
  isolation: isolate;
}
.tbs-hero-bg {
  position: absolute;
  inset: 0;
  z-index: -1;
  overflow: hidden;
}
.tbs-hero-glow-1,
.tbs-hero-glow-2 {
  position: absolute;
  border-radius: 50%;
  filter: blur(60px);
  opacity: 0.55;
  pointer-events: none;
}
.tbs-hero-glow-1 {
  width: 420px;
  height: 420px;
  top: -180px;
  right: -80px;
  background: radial-gradient(circle, rgba(167,139,250,0.9), transparent 70%);
}
.tbs-hero-glow-2 {
  width: 340px;
  height: 340px;
  bottom: -160px;
  left: -60px;
  background: radial-gradient(circle, rgba(99,102,241,0.9), transparent 70%);
}
.tbs-hero-grid {
  position: absolute;
  inset: 0;
  background-image: linear-gradient(rgba(255,255,255,0.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,0.05) 1px, transparent 1px);
  background-size: 44px 44px;
  -webkit-mask-image: radial-gradient(ellipse at center, #000 30%, transparent 75%);
  mask-image: radial-gradient(ellipse at center, #000 30%, transparent 75%);
  pointer-events: none;
}
.tbs-hero-inner { max-width: 860px; margin: 0 auto; position: relative; }
.tbs-hero-kicker {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 14px;
  border-radius: var(--tbs-r-pill);
  background: rgba(255,255,255,0.14);
  border: 1px solid rgba(255,255,255,0.22);
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: #fff;
  margin-bottom: 18px;
}
.tbs-hero-kicker svg { width: 15px; height: 15px; flex-shrink: 0; }
.tbs-hero h1 {
  font-size: clamp(1.9rem, 4.5vw, 2.9rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.1;
  margin-bottom: 12px;
  color: #fff;
}
.tbs-hero p {
  font-size: clamp(0.95rem, 1.3vw, 1.0625rem);
  color: rgba(255,255,255,0.82);
  max-width: 620px;
  margin: 0 auto 28px;
  line-height: 1.7;
}
body.tbs-dark .tbs-hero { background: linear-gradient(135deg, #14102e 0%, #2d2a63 55%, #4c2a7a 100%); }

/* ─── Glass Search Bar ─── */
.tbs-search-wrap {
  max-width: 700px;
  margin: 0 auto;
  position: relative;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 6px 6px 6px 18px;
  border-radius: 16px;
  background: rgba(255,255,255,0.12);
  border: 1px solid rgba(255,255,255,0.22);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  transition: background 250ms var(--tbs-ease), border-color 250ms var(--tbs-ease), box-shadow 250ms var(--tbs-ease);
}
.tbs-search-wrap:focus-within {
  background: rgba(255,255,255,0.16);
  border-color: rgba(255,255,255,0.45);
  box-shadow: 0 10px 30px -8px rgba(0,0,0,0.35);
}
.tbs-search-input {
  flex: 1;
  min-width: 0;
  height: 46px;
  padding: 0 12px;
  border: none;
  border-radius: 0;
  font-size: 15px;
  font-family: var(--tbs-font);
  background: transparent;
  color: #fff;
  outline: none;
  box-shadow: none;
}
.tbs-search-input::placeholder { color: rgba(255,255,255,0.55); }
.tbs-search-icon {
  position: static;
  transform: none;
  color: rgba(255,255,255,0.7);
  pointer-events: none;
  display: flex;
  flex-shrink: 0;
}
.tbs-search-icon svg { width: 20px; height: 20px; }
.tbs-search-btn {
  position: static;
  transform: none;
  height: 40px;
  padding: 0 24px;
  background: #fff;
  color: var(--tbs-primary-hover);
  border: none;
  border-radius: 12px;
  font-size: 14px;
  font-weight: 700;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  flex-shrink: 0;
  box-shadow: 0 4px 14px -4px rgba(0,0,0,0.3);
}
.tbs-search-btn:hover { transform: translateY(-1px); box-shadow: 0 8px 20px -6px rgba(0,0,0,0.35); }
.tbs-search-btn svg { color: currentColor; }

/* ─── Hero Meta Chips ─── */
.tbs-hero-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
  margin-top: 26px;
}
.tbs-hero-meta span {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 7px 14px;
  border-radius: var(--tbs-r-pill);
  background: rgba(255,255,255,0.1);
  border: 1px solid rgba(255,255,255,0.16);
  font-size: 0.78rem;
  font-weight: 500;
  color: rgba(255,255,255,0.85);
}
.tbs-hero-meta span svg { width: 14px; height: 14px; opacity: 0.7; }

/* ─── Filters row (legacy / unused on library page) ─── */
.tbs-filters {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  flex-wrap: wrap;
  position: relative;
  margin-top: 22px;
}
.tbs-filter-select {
  height: 42px;
  padding: 0 38px 0 14px;
  border: 1px solid rgba(255,255,255,0.25);
  border-radius: var(--tbs-r-sm);
  font-size: 14px;
  font-weight: 700;
  font-family: var(--tbs-font);
  background: rgba(255,255,255,0.1);
  color: #fff;
  cursor: pointer;
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg width='10' height='6' viewBox='0 0 10 6' fill='none' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M1 1L5 5L9 1' stroke='%23ffffff' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 14px center;
  transition: all 250ms var(--tbs-ease);
  outline: none;
  min-width: 160px;
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
}
.tbs-filter-select option { color: var(--tbs-text); background: var(--tbs-card); }
.tbs-filter-select:focus { border-color: rgba(255,255,255,0.55); box-shadow: 0 0 0 3px rgba(255,255,255,0.15); }

/* ═══════════════════════════════════════════
   CONTAINER & SECTION
   ═══════════════════════════════════════════ */
.tbs-container { max-width: 1320px; margin: 0 auto; padding: 0 32px; }
.tbs-section { padding: 40px 0; }

/* ─── Library Layout: Sidebar + Grid ─── */
.tbs-library-layout {
  display: grid;
  grid-template-columns: 264px 1fr;
  gap: 28px;
  align-items: start;
}
.tbs-filter-sidebar {
  position: sticky;
  top: calc(0px + 16px);
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-lg);
  padding: 22px;
  box-shadow: var(--tbs-shadow);
}
.tbs-filter-sidebar-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 20px;
  padding-bottom: 14px;
  border-bottom: 1px solid var(--tbs-border);
}
.tbs-filter-sidebar-header h3 {
  font-size: 15px;
  font-weight: 700;
  color: var(--tbs-text);
  display: flex;
  align-items: center;
  gap: 8px;
  margin: 0;
}
.tbs-filter-sidebar-header h3 svg { color: var(--tbs-primary); }
.tbs-filter-clear {
  font-size: 12px;
  font-weight: 600;
  color: var(--tbs-primary);
  background: none;
  border: none;
  cursor: pointer;
  font-family: var(--tbs-font);
  padding: 0;
}
.tbs-filter-clear:hover { text-decoration: underline; }
.tbs-filter-group { margin-bottom: 18px; }
.tbs-filter-label {
  display: block;
  font-size: 12px;
  font-weight: 600;
  color: var(--tbs-text-2);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 8px;
}
.tbs-filter-sidebar .tbs-filter-select {
  width: 100%;
  height: 40px;
  padding: 0 12px;
  background: var(--tbs-card-soft);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
  color: var(--tbs-text);
  font-size: 13px;
  font-weight: 500;
  font-family: var(--tbs-font);
  cursor: pointer;
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg width='12' height='12' viewBox='0 0 24 24' fill='none' stroke='%236B7280' stroke-width='2.5' xmlns='http://www.w3.org/2000/svg'%3E%3Cpolyline points='6 9 12 15 18 9'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  box-shadow: var(--tbs-shadow-sm);
  transition: all 250ms var(--tbs-ease);
}
.tbs-filter-sidebar .tbs-filter-select:focus { border-color: var(--tbs-primary); box-shadow: 0 0 0 3px var(--tbs-primary-glow); outline: none; }
.tbs-filter-stats {
  margin-top: 16px;
  padding-top: 14px;
  border-top: 1px solid var(--tbs-border);
  font-size: 12px;
  font-weight: 500;
  color: var(--tbs-text-3);
  text-align: center;
}
.tbs-filter-toggle-btn {
  display: none;
  align-items: center;
  gap: 6px;
  height: 36px;
  padding: 0 14px;
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
  color: var(--tbs-text-2);
  font-size: 13px;
  font-weight: 500;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 200ms var(--tbs-ease);
}
.tbs-filter-toggle-btn:hover { border-color: var(--tbs-primary); color: var(--tbs-primary); }

.tbs-section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 24px;
}
.tbs-section-title {
  font-size: 13px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--tbs-text-3);
}

/* ═══════════════════════════════════════════
   CONTINUE LEARNING CARD
   ═══════════════════════════════════════════ */
.tbs-continue-card {
  background: linear-gradient(135deg, var(--tbs-primary) 0%, #7C3AED 100%);
  border-radius: var(--tbs-r-lg);
  padding: 26px;
  color: #fff;
  box-shadow: 0 10px 28px -8px color-mix(in srgb, var(--tbs-primary) 55%, transparent);
  position: relative;
  overflow: hidden;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
  display: flex;
  flex-direction: column;
  gap: 12px;
  height: 100%;
}
.tbs-continue-card:hover { transform: translateY(-3px); box-shadow: 0 16px 40px -10px color-mix(in srgb, var(--tbs-primary) 65%, transparent); }
.tbs-continue-card::before {
  content: '';
  position: absolute;
  top: -40px;
  right: -30px;
  width: 120px;
  height: 120px;
  background: rgba(255,255,255,0.1);
  border-radius: 50%;
  filter: blur(2px);
}
.tbs-continue-label {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1px;
  opacity: 0.75;
}
.tbs-continue-book { font-size: 16px; font-weight: 700; line-height: 1.3; }
.tbs-continue-meta { font-size: 13px; opacity: 0.8; }
.tbs-continue-progress { width: 100%; height: 6px; background: rgba(255,255,255,0.2); border-radius: 3px; overflow: hidden; margin-top: auto; }
.tbs-continue-progress-fill { height: 100%; background: #fff; border-radius: 3px; transition: width 0.8s var(--tbs-ease); }
.tbs-continue-pct { font-size: 12px; font-weight: 600; opacity: 0.85; text-align: right; }
.tbs-continue-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  height: 40px;
  padding: 0 20px;
  background: rgba(255,255,255,0.2);
  -webkit-backdrop-filter: blur(8px);
  backdrop-filter: blur(8px);
  border: 1px solid rgba(255,255,255,0.25);
  border-radius: var(--tbs-r-sm);
  color: #fff;
  font-size: 13px;
  font-weight: 600;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
}
.tbs-continue-btn:hover { background: rgba(255,255,255,0.3); }

/* ═══════════════════════════════════════════
   BOOK GRID
   ═══════════════════════════════════════════ */
.tbs-book-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 22px;
}
.tbs-book-card {
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-lg);
  overflow: hidden;
  box-shadow: var(--tbs-shadow);
  transition: all 250ms var(--tbs-ease);
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: inherit;
}
.tbs-book-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--tbs-shadow-md);
  border-color: var(--tbs-primary-border);
}
.tbs-book-cover {
  width: 100%;
  aspect-ratio: 4/3;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  overflow: hidden;
}
.tbs-book-cover::after {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, rgba(0,0,0,0) 55%, rgba(0,0,0,0.18) 100%);
  pointer-events: none;
}
.tbs-book-cover img { transition: transform 400ms var(--tbs-ease); }
.tbs-book-card:hover .tbs-book-cover img { transform: scale(1.05); }
.tbs-book-cover-fallback {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
  text-align: center;
  padding: 20px;
}
.tbs-book-cover-fallback-title {
  font-size: 14px;
  font-weight: 600;
  color: rgba(255,255,255,0.95);
  line-height: 1.3;
  text-shadow: 0 1px 3px rgba(0,0,0,0.2);
  max-width: 90%;
}
.tbs-book-body { padding: 18px 20px 20px; flex: 1; display: flex; flex-direction: column; align-items: center; text-align: center; }
.tbs-book-title { font-size: 15px; font-weight: 700; color: var(--tbs-text); margin-bottom: 2px; line-height: 1.35; display: block; transition: color 250ms var(--tbs-ease); }
.tbs-book-card:hover .tbs-book-title { color: var(--tbs-primary); }
.tbs-book-class {
  display: inline-flex;
  align-items: center;
  margin-top: 8px;
  padding: 4px 12px;
  border-radius: var(--tbs-r-pill);
  background: var(--tbs-primary-soft);
  border: 1px solid var(--tbs-primary-border);
  color: var(--tbs-primary);
  font-size: 12px;
  font-weight: 600;
}
.tbs-book-author { font-size: 13px; color: var(--tbs-text-2); margin-bottom: 2px; }
.tbs-book-meta { font-size: 12px; color: var(--tbs-text-3); margin-bottom: 10px; }
.tbs-book-stats {
  display: flex;
  gap: 14px;
  font-size: 12px;
  color: var(--tbs-text-3);
  font-weight: 500;
  margin-bottom: 12px;
}
.tbs-book-stats span { display: inline-flex; align-items: center; gap: 4px; padding: 3px 10px; border-radius: var(--tbs-r-pill); background: var(--tbs-card-soft); border: 1px solid var(--tbs-border); }
.tbs-book-progress { width: 100%; height: 5px; background: var(--tbs-border-light); border-radius: 3px; overflow: hidden; margin-bottom: 6px; }
.tbs-book-progress-fill { height: 100%; background: var(--tbs-primary); border-radius: 3px; transition: width 0.8s var(--tbs-ease); }
.tbs-book-pct { font-size: 12px; font-weight: 600; color: var(--tbs-primary); margin-bottom: 12px; }
.tbs-book-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: auto;
  padding-top: 14px;
  border-top: 1px solid var(--tbs-border-light);
}
.tbs-book-bmk {
  width: 34px;
  height: 34px;
  border-radius: 10px;
  border: 1px solid var(--tbs-border);
  background: transparent;
  color: var(--tbs-text-3);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
}
.tbs-book-bmk:hover { color: var(--tbs-primary); border-color: var(--tbs-primary); background: var(--tbs-primary-soft); }
.tbs-book-bmk.tbs-active { color: var(--tbs-primary); border-color: var(--tbs-primary); background: var(--tbs-primary-soft); }
.tbs-book-bmk svg { width: 16px; height: 16px; }
.tbs-book-open {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  height: 40px;
  padding: 0 20px;
  background: linear-gradient(135deg, var(--tbs-primary) 0%, var(--tbs-primary-hover) 100%);
  color: #fff !important;
  border: none;
  border-radius: var(--tbs-r-sm);
  font-size: 14px;
  font-weight: 800 !important;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
  letter-spacing: 0.02em;
  text-transform: none;
  box-shadow: 0 4px 12px -4px color-mix(in srgb, var(--tbs-primary) 45%, transparent);
}
.tbs-book-open:hover { transform: translateY(-1px); box-shadow: 0 8px 18px -6px color-mix(in srgb, var(--tbs-primary) 55%, transparent); }

/* ─── Load More ─── */
.tbs-load-more { text-align: center; padding: 36px 0 16px; }
.tbs-load-more-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 12px 28px;
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-pill);
  font-size: 14px;
  font-weight: 600;
  color: var(--tbs-text-2);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  font-family: var(--tbs-font);
  box-shadow: var(--tbs-shadow-sm);
}
.tbs-load-more-btn:hover { color: var(--tbs-primary); border-color: var(--tbs-primary-border); background: var(--tbs-primary-soft); transform: translateY(-2px); box-shadow: var(--tbs-shadow-md); }
.tbs-load-more-btn svg { width: 16px; height: 16px; }

/* ═══════════════════════════════════════════
   THREE-COLUMN LAYOUT
   ═══════════════════════════════════════════ */
.tbs-layout {
  display: grid;
  grid-template-columns: var(--tbs-sidebar-w) 1fr var(--tbs-right-w);
  gap: 0;
  min-height: calc(100vh - 0px);
}

/* ─── Left Sidebar ─── */
.tbs-left-sidebar {
  position: sticky;
  top: 0px;
  height: calc(100vh - 0px);
  overflow-y: auto;
  background: var(--tbs-card);
  border-right: 1px solid var(--tbs-border);
  padding: 24px 0;
  scrollbar-width: thin;
}
.tbs-left-sidebar::-webkit-scrollbar { width: 4px; }
.tbs-left-sidebar::-webkit-scrollbar-thumb { background: var(--tbs-border); border-radius: 4px; }

.tbs-sidebar-book { padding: 0 20px 20px; }
.tbs-sidebar-cover {
  width: 100%;
  aspect-ratio: 4/3;
  border-radius: var(--tbs-r);
  overflow: hidden;
  margin-bottom: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--tbs-border-light);
}
.tbs-sidebar-cover img { width: 60%; height: 75%; object-fit: cover; border-radius: 6px; }
.tbs-sidebar-cover svg { width: 32px; height: 32px; color: rgba(255,255,255,0.7); }
.tbs-sidebar-title { font-size: 15px; font-weight: 700; color: var(--tbs-text); margin-bottom: 4px; line-height: 1.35; }
.tbs-sidebar-author { font-size: 13px; color: var(--tbs-text-2); margin-bottom: 2px; }
.tbs-sidebar-meta { font-size: 12px; color: var(--tbs-text-3); margin-bottom: 14px; }
.tbs-sidebar-view-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  width: 100%;
  height: 38px;
  background: transparent;
  border: 1px solid var(--tbs-primary-border);
  border-radius: var(--tbs-r-sm);
  color: var(--tbs-primary);
  font-size: 13px;
  font-weight: 600;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
  margin-bottom: 20px;
}
.tbs-sidebar-view-btn:hover { background: var(--tbs-primary-soft); }
.tbs-sidebar-view-btn svg { width: 14px; height: 14px; }

.tbs-sidebar-section-title {
  padding: 0 20px 8px;
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--tbs-text-3);
}
.tbs-chapter-list { list-style: none; }
.tbs-chapter-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 20px;
  font-size: 13px;
  font-weight: 500;
  color: var(--tbs-text-2);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  border-left: 3px solid transparent;
  text-decoration: none;
}
.tbs-chapter-item:hover { background: var(--tbs-card-soft); color: var(--tbs-text); }
.tbs-chapter-item.tbs-active {
  background: linear-gradient(135deg, var(--tbs-primary) 0%, var(--tbs-primary-hover) 100%);
  color: #fff;
  border-radius: 0 10px 10px 0;
  border-left-color: var(--tbs-primary);
  font-weight: 600;
}
.tbs-chapter-num {
  width: 24px;
  height: 24px;
  border-radius: 7px;
  background: var(--tbs-border-light);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 11px;
  font-weight: 700;
  flex-shrink: 0;
  color: var(--tbs-text-3);
}
.tbs-chapter-item.tbs-active .tbs-chapter-num { background: rgba(255,255,255,0.2); color: #fff; }
.tbs-chapter-expand {
  margin-left: auto;
  transition: transform 250ms var(--tbs-ease);
  color: var(--tbs-text-3);
  display: flex;
}
.tbs-chapter-expand svg { width: 14px; height: 14px; }
.tbs-chapter-item.tbs-expanded .tbs-chapter-expand { transform: rotate(90deg); }
.tbs-exercise-list { list-style: none; overflow: hidden; max-height: 0; transition: max-height 300ms var(--tbs-ease); }
.tbs-exercise-list.tbs-open { max-height: 600px; }
.tbs-exercise-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 20px 8px 54px;
  font-size: 12px;
  font-weight: 500;
  color: var(--tbs-text-3);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
}
.tbs-exercise-item:hover { color: var(--tbs-text); background: var(--tbs-card-soft); }
.tbs-exercise-item.tbs-active { color: var(--tbs-primary); font-weight: 600; background: var(--tbs-primary-soft); }

/* ─── Main Content ─── */
.tbs-main-content {
  padding: 28px 40px;
  min-height: 100%;
}
.tbs-breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--tbs-text-3);
  margin-bottom: 20px;
  flex-wrap: wrap;
}
.tbs-breadcrumb a { color: var(--tbs-text-2); transition: color 250ms var(--tbs-ease); }
.tbs-breadcrumb a:hover { color: var(--tbs-primary); }
.tbs-breadcrumb-sep { color: var(--tbs-border); font-size: 11px; }
.tbs-breadcrumb-current { color: var(--tbs-text); font-weight: 600; }

.tbs-page-header { margin-bottom: 24px; }
.tbs-page-title { font-size: 28px; font-weight: 800; letter-spacing: -0.03em; margin-bottom: 6px; }
.tbs-page-subtitle { font-size: 15px; color: var(--tbs-text-2); margin-bottom: 14px; }
.tbs-badges { display: flex; gap: 8px; flex-wrap: wrap; }
.tbs-badge {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 5px 12px;
  border-radius: var(--tbs-r-pill);
  font-size: 12px;
  font-weight: 600;
}
.tbs-badge-default { background: var(--tbs-card-soft); border: 1px solid var(--tbs-border); color: var(--tbs-text-2); }
.tbs-badge-warning { background: var(--tbs-warning-bg); border: 1px solid var(--tbs-warning-border); color: var(--tbs-warning); }
.tbs-badge-success { background: var(--tbs-success-bg); border: 1px solid var(--tbs-success-border); color: var(--tbs-success); }
.tbs-badge svg { width: 14px; height: 14px; }

/* ─── Exercise Cards ─── */
.tbs-exercise-cards { display: flex; flex-direction: column; gap: 10px; }
.tbs-exercise-card {
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r);
  padding: 18px 22px;
  display: flex;
  align-items: center;
  gap: 16px;
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
  color: inherit;
  box-shadow: var(--tbs-shadow);
}
.tbs-exercise-card:hover { border-color: var(--tbs-primary-border); background: var(--tbs-card); transform: translateX(4px); box-shadow: var(--tbs-shadow-md); }
.tbs-exercise-card-num {
  width: 42px;
  height: 42px;
  border-radius: 12px;
  background: var(--tbs-primary-soft);
  color: var(--tbs-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 15px;
  font-weight: 700;
  flex-shrink: 0;
  transition: all 250ms var(--tbs-ease);
}
.tbs-exercise-card:hover .tbs-exercise-card-num { background: var(--tbs-primary); color: #fff; }
.tbs-exercise-card-info { flex: 1; }
.tbs-exercise-card-title { font-size: 15px; font-weight: 600; color: var(--tbs-text); margin-bottom: 2px; }
.tbs-exercise-card-meta { font-size: 12px; color: var(--tbs-text-3); }
.tbs-exercise-card-arrow { color: var(--tbs-text-3); transition: all 250ms var(--tbs-ease); display: flex; flex-shrink: 0; }
.tbs-exercise-card:hover .tbs-exercise-card-arrow { color: var(--tbs-primary); transform: translateX(4px); }

/* ─── Chapter Cards ─── */
.tbs-chapter-cards { display: flex; flex-direction: column; gap: 10px; }
.tbs-chapter-card {
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r);
  padding: 18px 22px;
  display: flex;
  align-items: center;
  gap: 16px;
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
  color: inherit;
  box-shadow: var(--tbs-shadow);
}
.tbs-chapter-card:hover { border-color: var(--tbs-primary-border); transform: translateX(4px); box-shadow: var(--tbs-shadow-md); }
.tbs-chapter-card-num {
  width: 42px;
  height: 42px;
  border-radius: 12px;
  background: linear-gradient(135deg, var(--tbs-primary) 0%, var(--tbs-primary-hover) 100%);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 15px;
  font-weight: 700;
  flex-shrink: 0;
}
.tbs-chapter-card-info { flex: 1; }
.tbs-chapter-card-title { font-size: 15px; font-weight: 600; color: var(--tbs-text); margin-bottom: 2px; }
.tbs-chapter-card-desc { font-size: 13px; color: var(--tbs-text-2); margin-bottom: 4px; }
.tbs-chapter-card-meta { font-size: 12px; color: var(--tbs-text-3); }
.tbs-chapter-card-arrow { color: var(--tbs-text-3); transition: all 250ms var(--tbs-ease); display: flex; flex-shrink: 0; }
.tbs-chapter-card:hover .tbs-chapter-card-arrow { color: var(--tbs-primary); transform: translateX(4px); }

/* ─── Right Sidebar ─── */
.tbs-right-sidebar {
  position: sticky;
  top: 0px;
  height: calc(100vh - 0px);
  overflow-y: auto;
  background: var(--tbs-card);
  border-left: 1px solid var(--tbs-border);
  padding: 24px 16px;
  scrollbar-width: thin;
}
.tbs-right-sidebar::-webkit-scrollbar { width: 4px; }
.tbs-right-sidebar::-webkit-scrollbar-thumb { background: var(--tbs-border); border-radius: 4px; }
.tbs-rs-title {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--tbs-text-3);
  margin-bottom: 12px;
}
.tbs-q-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 6px;
  margin-bottom: 20px;
}
.tbs-q-nav-btn {
  width: 100%;
  aspect-ratio: 1;
  border-radius: 9px;
  border: 1px solid var(--tbs-border);
  background: var(--tbs-card);
  color: var(--tbs-text-2);
  font-size: 12px;
  font-weight: 600;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  display: flex;
  align-items: center;
  justify-content: center;
}
.tbs-q-nav-btn:hover { border-color: var(--tbs-primary); color: var(--tbs-primary); background: var(--tbs-primary-soft); }
.tbs-q-nav-btn.tbs-active { background: var(--tbs-primary); color: #fff; border-color: var(--tbs-primary); box-shadow: 0 2px 8px color-mix(in srgb, var(--tbs-primary) 35%, transparent); }

/* ─── Bookmark Card ─── */
.tbs-rs-card {
  background: var(--tbs-card-soft);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r);
  padding: 16px;
  margin-bottom: 16px;
  text-align: center;
}
.tbs-rs-card-title { font-size: 12px; font-weight: 600; color: var(--tbs-text-2); margin-bottom: 8px; }
.tbs-rs-card .tbs-btn { width: 100%; }

/* ─── Prev/Next Nav ─── */
.tbs-rs-nav { display: flex; flex-direction: column; gap: 8px; margin-bottom: 16px; }
.tbs-rs-nav-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 14px;
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
  font-size: 12px;
  font-weight: 500;
  color: var(--tbs-text-2);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
}
.tbs-rs-nav-btn:hover { border-color: var(--tbs-primary); color: var(--tbs-primary); background: var(--tbs-primary-soft); }
.tbs-rs-nav-btn svg { width: 14px; height: 14px; flex-shrink: 0; }

/* ═══════════════════════════════════════════
   EXERCISE PAGE — Questions
   ═══════════════════════════════════════════ */
.tbs-exercise-controls {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}

/* ─── Question Cards ─── */
.tbs-questions-list { display: flex; flex-direction: column; gap: 14px; }
.tbs-question-card {
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-lg);
  padding: 24px;
  transition: all 250ms var(--tbs-ease);
  scroll-margin-top: calc(0px + 20px);
  box-shadow: var(--tbs-shadow);
}
.tbs-question-card:target,
.tbs-question-card.tbs-highlight { border-color: var(--tbs-primary); box-shadow: var(--tbs-shadow-glow); }
.tbs-question-header {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
  row-gap: 8px;
  margin-bottom: 16px;
}
.tbs-question-number {
  width: 36px;
  height: 36px;
  border-radius: 11px;
  background: linear-gradient(135deg, var(--tbs-primary) 0%, var(--tbs-primary-hover) 100%);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 14px;
  font-weight: 700;
  flex-shrink: 0;
  box-shadow: 0 3px 10px -3px color-mix(in srgb, var(--tbs-primary) 50%, transparent);
}
.tbs-question-type-badge {
  padding: 3px 10px;
  border-radius: var(--tbs-r-pill);
  font-size: 11px;
  font-weight: 600;
}
.tbs-type-objective { background: var(--tbs-primary-soft); color: var(--tbs-primary); }
.tbs-type-theory { background: #F3E8FF; color: #7C3AED; }
.tbs-type-math { background: var(--tbs-success-bg); color: var(--tbs-success); }
.tbs-type-fill_blank { background: var(--tbs-warning-bg); color: var(--tbs-warning); }
.tbs-type-true_false { background: var(--tbs-danger-bg); color: var(--tbs-danger); }
.tbs-question-difficulty {
  padding: 3px 10px;
  border-radius: var(--tbs-r-pill);
  font-size: 11px;
  font-weight: 600;
  background: var(--tbs-card-soft);
  color: var(--tbs-text-3);
  border: 1px solid var(--tbs-border);
}
.tbs-icon-btn {
  width: 32px;
  height: 32px;
  border-radius: 9px;
  border: 1px solid var(--tbs-border);
  background: transparent;
  color: var(--tbs-text-3);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  margin-left: auto;
  flex-shrink: 0;
}
.tbs-icon-btn:hover { color: var(--tbs-primary); border-color: var(--tbs-primary); background: var(--tbs-primary-soft); }
.tbs-icon-btn svg { width: 16px; height: 16px; }
.tbs-question-actions { margin-left: auto; display: flex; align-items: center; gap: 8px; }
.tbs-question-actions .tbs-icon-btn { margin-left: 0; }
.tbs-share-btn:hover { color: var(--tbs-primary); border-color: var(--tbs-primary); background: var(--tbs-primary-soft); }
.tbs-icon-btn.tbs-bookmark-pending { opacity: 0.6; pointer-events: none; }

/* ─── Toast ─── */
.tbs-toast {
  position: fixed;
  left: 50%;
  bottom: 24px;
  transform: translateX(-50%) translateY(16px);
  z-index: 99999;
  max-width: calc(100vw - 32px);
  padding: 12px 18px;
  border-radius: 12px;
  background: var(--tbs-card);
  color: var(--tbs-text);
  border: 1px solid var(--tbs-border);
  box-shadow: 0 16px 40px -12px rgba(0, 0, 0, 0.28);
  font-size: 13px;
  font-weight: 600;
  opacity: 0;
  pointer-events: none;
  transition: opacity 250ms var(--tbs-ease), transform 250ms var(--tbs-ease);
}
.tbs-toast.tbs-toast-visible { opacity: 1; transform: translateX(-50%) translateY(0); }
.tbs-toast.tbs-toast-error { color: var(--tbs-danger); background: var(--tbs-danger-bg); border-color: var(--tbs-border); }

.tbs-question-content { font-size: 15px; line-height: 1.75; color: var(--tbs-text); margin-bottom: 16px; }
.tbs-question-content p { margin-bottom: 8px; }
.tbs-question-images { display: flex; gap: 12px; flex-wrap: wrap; margin-bottom: 16px; }
.tbs-question-images img { max-width: 100%; max-height: 300px; border-radius: var(--tbs-r-sm); border: 1px solid var(--tbs-border); }

/* ─── Solution Toggle ─── */
.tbs-solution-toggle { margin-bottom: 4px; }
.tbs-solution-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  height: 40px;
  padding: 0 20px;
  border-radius: var(--tbs-r-sm);
  font-size: 13px;
  font-weight: 600;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  border: 1px solid var(--tbs-primary);
  background: transparent;
  color: var(--tbs-primary);
}
.tbs-solution-btn:hover { background: var(--tbs-primary-soft); }
.tbs-solution-btn svg { width: 16px; height: 16px; }
.tbs-solution-btn.tbs-open { background: linear-gradient(135deg, var(--tbs-primary) 0%, var(--tbs-primary-hover) 100%); color: #fff; border-color: var(--tbs-primary); box-shadow: 0 3px 10px -3px color-mix(in srgb, var(--tbs-primary) 45%, transparent); }

/* ─── Solution Area ─── */
.tbs-solution-area { max-height: 0; overflow: hidden; transition: max-height 350ms var(--tbs-ease), opacity 250ms ease, margin 250ms ease; opacity: 0; margin-top: 0; }
.tbs-solution-area.tbs-open { max-height: 20000px; opacity: 1; margin-top: 16px; }
.tbs-solution-box { background: var(--tbs-success-bg); border: 1px solid var(--tbs-success-border); border-radius: var(--tbs-r-lg); padding: 24px; }
.tbs-solution-heading {
  font-size: 13px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--tbs-success);
  margin-bottom: 14px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.tbs-solution-heading svg { width: 16px; height: 16px; }
.tbs-solution-content { font-size: 14px; line-height: 1.85; color: var(--tbs-text); }
.tbs-solution-content p { margin-bottom: 10px; }
.tbs-solution-video { margin-top: 16px; }
.tbs-solution-video a { text-decoration: none; }
.tbs-solution-unavailable { color: var(--tbs-text-3); font-style: italic; }

/* ─── Solution Comments ─── */
.tbs-solution-comments { margin-top: 24px; padding-top: 20px; border-top: 1px dashed var(--tbs-success-border); }
.tbs-comments-head {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--tbs-success);
  margin-bottom: 14px;
}
.tbs-comments-head svg { width: 15px; height: 15px; }
.tbs-comments-count {
  min-width: 22px;
  height: 20px;
  padding: 0 6px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--tbs-r-pill);
  background: var(--tbs-success);
  color: #fff;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0;
  text-transform: none;
}
.tbs-comments-list { display: flex; flex-direction: column; gap: 12px; margin-bottom: 16px; }
.tbs-comments-empty { font-size: 13px; color: var(--tbs-text-3); font-style: italic; }
.tbs-comment-item {
  display: flex;
  gap: 12px;
  padding: 14px 16px;
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
}
.tbs-comment-avatar {
  width: 36px;
  height: 36px;
  flex-shrink: 0;
  border-radius: 50%;
  color: #fff;
  font-size: 14px;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  text-transform: uppercase;
}
.tbs-comment-body { flex: 1; min-width: 0; }
.tbs-comment-meta { display: flex; align-items: baseline; gap: 8px; margin-bottom: 4px; flex-wrap: wrap; }
.tbs-comment-author { font-size: 13px; font-weight: 700; color: var(--tbs-text); }
.tbs-comment-time { font-size: 11px; color: var(--tbs-text-3); }
.tbs-comment-content { font-size: 13px; line-height: 1.7; color: var(--tbs-text-2); word-break: break-word; }
.tbs-comment-form { display: flex; flex-direction: column; align-items: flex-start; gap: 10px; }
.tbs-comment-input {
  width: 100%;
  min-height: 64px;
  padding: 12px 14px;
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
  background: var(--tbs-card);
  color: var(--tbs-text);
  font-family: var(--tbs-font);
  font-size: 13px;
  line-height: 1.6;
  resize: vertical;
  transition: border-color 200ms var(--tbs-ease), box-shadow 200ms var(--tbs-ease);
}
.tbs-comment-input:focus {
  outline: none;
  border-color: var(--tbs-primary);
  box-shadow: 0 0 0 3px var(--tbs-primary-glow);
}
.tbs-comment-input::placeholder { color: var(--tbs-text-3); }
.tbs-comment-submit { height: 38px; padding: 0 18px; font-size: 13px; }
.tbs-comment-submit svg { width: 14px; height: 14px; }
.tbs-comment-submit.tbs-loading { opacity: 0.65; pointer-events: none; }
.tbs-comment-login { font-size: 13px; color: var(--tbs-text-3); font-style: italic; margin: 0; }
.tbs-comment-status {
  font-size: 12px;
  font-weight: 600;
  color: var(--tbs-success);
  min-height: 16px;
}
.tbs-comment-status.tbs-comment-status-error { color: var(--tbs-danger); }

/* ─── Comment Actions (Reply / Follow) ─── */
.tbs-comment-actions {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 8px;
}
.tbs-comment-actions button {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 4px 10px;
  border: 1px solid var(--tbs-border);
  background: var(--tbs-card-soft);
  color: var(--tbs-text-2);
  font-family: var(--tbs-font);
  font-size: 12px;
  font-weight: 600;
  line-height: 1;
  border-radius: var(--tbs-r-pill);
  cursor: pointer;
  transition: all 200ms var(--tbs-ease);
}
.tbs-comment-actions button:hover { color: var(--tbs-primary); border-color: var(--tbs-primary-border); background: var(--tbs-primary-soft); }
.tbs-comment-actions button svg { width: 13px; height: 13px; }
.tbs-comment-actions .tbs-comment-reply-btn.tbs-active { color: var(--tbs-primary); border-color: var(--tbs-primary); background: var(--tbs-primary-soft); }
.tbs-comment-actions .tbs-follow-btn.tbs-following { color: var(--tbs-success); border-color: var(--tbs-success-border); background: var(--tbs-success-bg); }
.tbs-comment-actions .tbs-follow-btn.tbs-follow-pending { opacity: 0.6; pointer-events: none; }
.tbs-reply-count, .tbs-follow-count { font-weight: 700; }

/* ─── Reply Form ─── */
.tbs-comment-reply-form { display: none; flex-direction: column; gap: 10px; margin-top: 12px; }
.tbs-comment-reply-form.tbs-open { display: flex; }
.tbs-comment-reply-actions { display: flex; align-items: center; gap: 8px; }
.tbs-comment-reply-actions .tbs-btn { height: 36px; padding: 0 16px; font-size: 13px; }

/* ─── Nested Replies ─── */
.tbs-comment-replies { margin-top: 12px; padding-left: 10px; border-left: 2px solid var(--tbs-border); }
.tbs-comment-replies:empty { display: none; }
.tbs-comment-reply {
  padding: 12px 14px;
  background: var(--tbs-card-soft);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
}
.tbs-comment-reply .tbs-comment-avatar { width: 30px; height: 30px; font-size: 12px; }
.tbs-comment-reply .tbs-comment-actions button { padding: 3px 8px; font-size: 11px; }

/* ─── Share Popover ─── */
.tbs-share-popover {
  position: fixed;
  z-index: 99999;
  min-width: 230px;
  padding: 8px;
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-md);
  box-shadow: 0 16px 40px -12px rgba(0, 0, 0, 0.28);
  display: none;
  opacity: 0;
  transform: translateY(-6px);
  transition: opacity 180ms var(--tbs-ease), transform 180ms var(--tbs-ease);
}
.tbs-share-popover.tbs-open { display: block; opacity: 1; transform: translateY(0); }
.tbs-share-popover-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding: 6px 8px 8px;
  margin-bottom: 4px;
  border-bottom: 1px solid var(--tbs-border-light);
}
.tbs-share-popover-title {
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.4px;
  color: var(--tbs-text-3);
}
.tbs-share-popover-close {
  width: 24px;
  height: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 0;
  border-radius: 6px;
  background: transparent;
  color: var(--tbs-text-3);
  cursor: pointer;
  transition: all 200ms var(--tbs-ease);
}
.tbs-share-popover-close:hover { color: var(--tbs-danger); background: var(--tbs-danger-bg); }
.tbs-share-popover-grid { display: flex; flex-direction: column; gap: 2px; }
.tbs-share-opt {
  display: flex;
  align-items: center;
  gap: 10px;
  width: 100%;
  padding: 9px 10px;
  border: 0;
  border-radius: 8px;
  background: transparent;
  color: var(--tbs-text);
  font-family: var(--tbs-font);
  font-size: 13px;
  font-weight: 500;
  line-height: 1;
  text-decoration: none;
  cursor: pointer;
  transition: background 180ms var(--tbs-ease), color 180ms var(--tbs-ease);
}
.tbs-share-opt:hover { background: var(--tbs-card-soft); }
.tbs-share-opt svg { width: 16px; height: 16px; flex-shrink: 0; }
.tbs-share-opt[data-net="whatsapp"]:hover { color: #25D366; background: rgba(37, 211, 102, 0.12); }
.tbs-share-opt[data-net="facebook"]:hover { color: #1877F2; background: rgba(24, 119, 242, 0.12); }
.tbs-share-opt[data-net="x"]:hover { color: #71717A; background: rgba(113, 113, 122, 0.14); }
.tbs-share-opt[data-net="telegram"]:hover { color: #229ED9; background: rgba(34, 158, 217, 0.12); }
.tbs-share-copy { border-top: 1px solid var(--tbs-border-light); margin-top: 6px; padding-top: 10px; border-radius: 0 0 8px 8px; }
.tbs-share-copy.tbs-share-copied { color: var(--tbs-success); }
.tbs-share-copy.tbs-share-copied svg { color: var(--tbs-success); }

/* ─── Progress ─── */
.tbs-progress-section { margin-top: 16px; }
.tbs-progress-bar { width: 100%; height: 6px; background: var(--tbs-border-light); border-radius: 3px; overflow: hidden; margin-bottom: 8px; }
.tbs-progress-fill { height: 100%; background: var(--tbs-primary); border-radius: 3px; transition: width 0.6s var(--tbs-ease); }
.tbs-progress-text { font-size: 12px; color: var(--tbs-text-3); font-weight: 500; text-align: center; }

/* ─── Jump Select ─── */
.tbs-jump-select {
  width: 100%;
  height: 38px;
  padding: 0 32px 0 12px;
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
  font-size: 13px;
  font-weight: 500;
  font-family: var(--tbs-font);
  background: var(--tbs-card);
  color: var(--tbs-text);
  cursor: pointer;
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg width='10' height='6' viewBox='0 0 10 6' fill='none' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M1 1L5 5L9 1' stroke='%2394A3B8' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 10px center;
  margin-bottom: 16px;
  outline: none;
  transition: all 250ms var(--tbs-ease);
}
.tbs-jump-select:focus { border-color: var(--tbs-primary); box-shadow: 0 0 0 3px var(--tbs-primary-glow); }

/* ─── Kbd Bar ─── */
.tbs-kbd-bar {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 10px 14px;
  background: var(--tbs-card-soft);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
  margin-top: 16px;
}
.tbs-kbd { display: inline-flex; align-items: center; gap: 5px; font-size: 11px; color: var(--tbs-text-3); font-weight: 500; }
.tbs-kbd kbd {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 22px;
  height: 22px;
  padding: 0 6px;
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-bottom-width: 2px;
  border-radius: 6px;
  font-size: 11px;
  font-family: var(--tbs-font);
  font-weight: 600;
  color: var(--tbs-text-2);
}

/* ═══════════════════════════════════════════
   BUTTONS
   ═══════════════════════════════════════════ */
.tbs-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  height: 36px;
  padding: 0 16px;
  border-radius: var(--tbs-r-sm);
  font-size: 13px;
  font-weight: 600;
  font-family: var(--tbs-font);
  cursor: pointer;
  transition: all 250ms var(--tbs-ease);
  text-decoration: none;
  border: none;
  outline: none;
  white-space: nowrap;
}
.tbs-btn-primary { background: linear-gradient(135deg, var(--tbs-primary) 0%, var(--tbs-primary-hover) 100%); color: #fff; box-shadow: 0 3px 10px -3px color-mix(in srgb, var(--tbs-primary) 45%, transparent); }
.tbs-btn-primary:hover { transform: translateY(-1px); box-shadow: 0 6px 16px -4px color-mix(in srgb, var(--tbs-primary) 55%, transparent); }
.tbs-btn-outline { background: transparent; color: var(--tbs-primary); border: 1px solid var(--tbs-primary-border); }
.tbs-btn-outline:hover { background: var(--tbs-primary-soft); border-color: var(--tbs-primary); }
.tbs-btn-ghost { background: transparent; color: var(--tbs-text-2); border: 1px solid var(--tbs-border); }
.tbs-btn-ghost:hover { color: var(--tbs-text); background: var(--tbs-card-soft); border-color: var(--tbs-text-3); }

/* ═══════════════════════════════════════════
   MOBILE BOTTOM NAV
   ═══════════════════════════════════════════ */
.tbs-mobile-bottom-nav {
  display: none;
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  height: 64px;
  background: color-mix(in srgb, var(--tbs-card) 92%, transparent);
  -webkit-backdrop-filter: blur(20px);
  backdrop-filter: blur(20px);
  border-top: 1px solid var(--tbs-border);
  z-index: 100;
  padding: 0 16px;
  justify-content: space-around;
  align-items: center;
}
.tbs-mob-nav-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  padding: 6px 12px;
  border-radius: var(--tbs-r-sm);
  color: var(--tbs-text-3);
  font-size: 10px;
  font-weight: 500;
  text-decoration: none;
  transition: all 250ms var(--tbs-ease);
  cursor: pointer;
  border: none;
  background: none;
  font-family: var(--tbs-font);
}
.tbs-mob-nav-item svg { width: 20px; height: 20px; }
.tbs-mob-nav-item.tbs-active { color: var(--tbs-primary); }

/* ─── Mobile Drawer Trigger ─── */
.tbs-mobile-contents-btn,
.tbs-mobile-questions-btn { display: none; }

/* ─── Mobile Overlay ─── */
.tbs-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.35);
  -webkit-backdrop-filter: blur(4px);
  backdrop-filter: blur(4px);
  z-index: 200;
  opacity: 0;
  transition: opacity 300ms var(--tbs-ease);
}
.tbs-overlay.tbs-active { opacity: 1; }

/* ─── Empty State ─── */
.tbs-empty-state {
  text-align: center;
  padding: 64px 24px;
  color: var(--tbs-text-3);
  background: var(--tbs-card);
  border: 1px dashed var(--tbs-border);
  border-radius: var(--tbs-r-lg);
  box-shadow: var(--tbs-shadow);
}
.tbs-empty-state svg { width: 48px; height: 48px; margin-bottom: 16px; color: var(--tbs-primary); opacity: 0.35; }
.tbs-empty-state p { font-size: 15px; color: var(--tbs-text-2); }

/* ═══════════════════════════════════════════
   SEARCH RESULTS
   ═══════════════════════════════════════════ */
.tbs-search-group { margin-bottom: 32px; }
.tbs-search-group-title {
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--tbs-text-3);
  margin-bottom: 12px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--tbs-border-light);
}
.tbs-search-result-item {
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r);
  padding: 14px 18px;
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  gap: 14px;
  text-decoration: none;
  color: inherit;
  transition: all 250ms var(--tbs-ease);
  box-shadow: var(--tbs-shadow);
}
.tbs-search-result-item:hover { border-color: var(--tbs-primary-border); background: var(--tbs-card); transform: translateX(3px); box-shadow: var(--tbs-shadow-md); }
.tbs-search-result-icon {
  width: 38px;
  height: 38px;
  border-radius: 11px;
  background: var(--tbs-primary-soft);
  color: var(--tbs-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}
.tbs-search-result-icon svg { width: 18px; height: 18px; }
.tbs-search-result-info { flex: 1; }
.tbs-search-result-title { font-size: 14px; font-weight: 600; color: var(--tbs-text); margin-bottom: 2px; }
.tbs-search-result-meta { font-size: 12px; color: var(--tbs-text-3); }

/* ═══════════════════════════════════════════
   ANIMATIONS
   ═══════════════════════════════════════════ */
@keyframes tbs-fadeIn {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}
.tbs-fade-in { animation: tbs-fadeIn 0.5s var(--tbs-ease) forwards; }
.tbs-fade-in-delay-1 { animation-delay: 0.06s; opacity: 0; }
.tbs-fade-in-delay-2 { animation-delay: 0.12s; opacity: 0; }
.tbs-fade-in-delay-3 { animation-delay: 0.18s; opacity: 0; }
.tbs-fade-in-delay-4 { animation-delay: 0.24s; opacity: 0; }

/* ═══════════════════════════════════════════
   BACK TO TOP
   ═══════════════════════════════════════════ */
.tbs-back-top {
  position: fixed;
  bottom: 32px;
  right: 32px;
  width: 44px;
  height: 44px;
  border-radius: 13px;
  background: linear-gradient(135deg, var(--tbs-primary) 0%, var(--tbs-primary-hover) 100%);
  color: #fff;
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 6px 16px -4px color-mix(in srgb, var(--tbs-primary) 55%, transparent);
  transition: all 250ms var(--tbs-ease);
  opacity: 0;
  pointer-events: none;
  transform: translateY(12px);
  z-index: 50;
}
.tbs-back-top svg { width: 20px; height: 20px; }
.tbs-back-top.tbs-visible { opacity: 1; pointer-events: auto; transform: translateY(0); }
.tbs-back-top:hover { transform: translateY(-3px) scale(1.04); box-shadow: 0 10px 24px -6px color-mix(in srgb, var(--tbs-primary) 60%, transparent); }

/* ═══════════════════════════════════════════
   RESPONSIVE
   ═══════════════════════════════════════════ */
@media (max-width: 1100px) {
  .tbs-book-grid { grid-template-columns: repeat(3, 1fr); }
  .tbs-library-layout { grid-template-columns: 224px 1fr; gap: 20px; }
}
@media (max-width: 900px) {
  .tbs-book-grid { grid-template-columns: repeat(2, 1fr); }
  .tbs-layout { grid-template-columns: 1fr; }
  .tbs-library-layout { grid-template-columns: 1fr; }
  .tbs-filter-sidebar {
    position: fixed;
    top: 0;
    left: 0;
    height: 100vh;
    width: 300px;
    max-width: 85vw;
    z-index: 220;
    transform: translateX(-100%);
    transition: transform 350ms var(--tbs-ease);
    box-shadow: var(--tbs-shadow-xl);
    overflow-y: auto;
    padding-top: 24px;
    border-radius: 0;
  }
  .tbs-filter-sidebar.tbs-mobile-open { transform: translateX(0); }
  .tbs-filter-toggle-btn { display: inline-flex; }
  .tbs-left-sidebar, .tbs-right-sidebar {
    position: fixed;
    top: 0;
    height: 100vh;
    z-index: 210;
    transform: translateX(-100%);
    transition: transform 350ms var(--tbs-ease);
    width: 320px;
    max-width: 85vw;
    box-shadow: var(--tbs-shadow-xl);
  }
  .tbs-left-sidebar { left: 0; }
  .tbs-right-sidebar { right: 0; left: auto; transform: translateX(100%); }
  .tbs-left-sidebar.tbs-mobile-open { transform: translateX(0); }
  .tbs-right-sidebar.tbs-mobile-open { transform: translateX(0); }
  .tbs-mobile-contents-btn, .tbs-mobile-questions-btn { display: inline-flex; }
  .tbs-main-content { padding: 24px 20px 80px; }
  .tbs-hero { padding: 40px 20px 32px; }
  .tbs-hero h1 { font-size: 28px; }
  .tbs-hero p { font-size: 15px; }
  .tbs-container { padding: 0 20px; }
  .tbs-page-title { font-size: 22px; }
  .tbs-question-card { padding: 18px; }
  .tbs-back-top { bottom: 80px; }
}
@media (max-width: 600px) {
  .tbs-book-grid { grid-template-columns: 1fr; }
  .tbs-filters { flex-direction: column; }
  .tbs-filter-select { width: 100%; }
  .tbs-search-btn { width: 100%; height: 46px; margin-top: 8px; }
  .tbs-search-wrap { flex-direction: column; padding: 12px; }
  .tbs-search-input { width: 100%; }
  .tbs-exercise-controls { flex-direction: column; }
  .tbs-exercise-controls .tbs-btn { width: 100%; }
  .tbs-back-top { bottom: 80px; right: 16px; }
  .tbs-mobile-contents-btn, .tbs-mobile-questions-btn {
    display: inline-flex;
    position: fixed;
    bottom: 76px;
    height: 44px;
    padding: 0 18px;
    background: var(--tbs-card);
    border: 1px solid var(--tbs-border);
    border-radius: var(--tbs-r-pill);
    font-size: 13px;
    font-weight: 600;
    font-family: var(--tbs-font);
    color: var(--tbs-text);
    cursor: pointer;
    box-shadow: var(--tbs-shadow-lg);
    z-index: 50;
    gap: 6px;
    align-items: center;
  }
  .tbs-mobile-contents-btn { left: 16px; }
  .tbs-mobile-questions-btn { right: 16px; background: var(--tbs-primary); color: #fff; border: none; }
  .tbs-mobile-contents-btn svg { width: 16px; height: 16px; }
}

/* ─── Print ─── */
@media print {
  .tbs-left-sidebar, .tbs-right-sidebar, .tbs-back-top,
  .tbs-mobile-contents-btn, .tbs-mobile-questions-btn, .tbs-mobile-bottom-nav,
  .tbs-solution-toggle, .tbs-exercise-controls, .tbs-overlay,
  .tbs-search-wrap, .tbs-filters, .tbs-topbar { display: none !important; }
  .tbs-layout { grid-template-columns: 1fr !important; }
  .tbs-main-content { padding: 0 !important; }
  .tbs-solution-area { max-height: none !important; opacity: 1 !important; overflow: visible !important; }
  .tbs-question-card { break-inside: avoid; page-break-inside: avoid; border: 1px solid #ddd; }
  .tbs-book-card { break-inside: avoid; page-break-inside: avoid; }
}

/* ─── Staggered Animation ─── */
.tbs-stagger-item {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.5s cubic-bezier(0.4,0,0.2,1), transform 0.5s cubic-bezier(0.4,0,0.2,1);
}
.tbs-stagger-item.tbs-stagger-visible {
  opacity: 1;
  transform: translateY(0);
}

/* ─── Top Navigation Bar ─── */
.tbs-topbar {
  position: sticky;
  top: 0;
  z-index: 100;
  background: color-mix(in srgb, var(--tbs-card) 88%, transparent);
  -webkit-backdrop-filter: blur(16px);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--tbs-border);
  box-shadow: var(--tbs-shadow);
}
.tbs-topbar-inner {
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 24px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}
.tbs-topbar-back {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 14px;
  font-weight: 600;
  color: var(--tbs-text);
  text-decoration: none;
  padding: 6px 14px;
  border-radius: var(--tbs-r-sm);
  border: 1px solid var(--tbs-border);
  background: var(--tbs-card);
  transition: all 200ms var(--tbs-ease);
  white-space: nowrap;
  flex-shrink: 0;
}
.tbs-topbar-back:hover {
  color: var(--tbs-primary);
  border-color: var(--tbs-primary);
  background: var(--tbs-primary-soft);
}
.tbs-topbar-search {
  display: flex;
  align-items: center;
  gap: 8px;
  flex: 1;
  max-width: 400px;
  background: var(--tbs-card-soft);
  border: 1px solid var(--tbs-border);
  border-radius: var(--tbs-r-sm);
  padding: 0 12px;
  height: 36px;
  transition: border-color 200ms var(--tbs-ease);
}
.tbs-topbar-search:focus-within {
  border-color: var(--tbs-primary);
  box-shadow: 0 0 0 3px var(--tbs-primary-glow);
}
.tbs-topbar-search svg { color: var(--tbs-text-3); flex-shrink: 0; }
.tbs-topbar-search-input {
  border: none;
  background: transparent;
  outline: none;
  font-size: 13px;
  font-family: var(--tbs-font);
  color: var(--tbs-text);
  width: 100%;
}
.tbs-topbar-search-input::placeholder { color: var(--tbs-text-3); }
@media (max-width: 600px) {
  .tbs-topbar-search { max-width: none; }
  .tbs-topbar-back span { display: none; }
}

/* ─── You Might Also Like ─── */
.tbs-related-section {
  margin-top: 48px;
  padding-top: 36px;
  border-top: 1px solid var(--tbs-border);
}
.tbs-related-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 18px;
  font-weight: 700;
  color: var(--tbs-text);
  margin-bottom: 20px;
}
.tbs-related-title svg { color: var(--tbs-primary); }
.tbs-related-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
}
@media (max-width: 900px) {
  .tbs-related-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 480px) {
  .tbs-related-grid { grid-template-columns: 1fr; }
}
.tbs-related-card {
  display: flex;
  flex-direction: column;
  border-radius: var(--tbs-r-lg);
  overflow: hidden;
  background: var(--tbs-card);
  border: 1px solid var(--tbs-border);
  text-decoration: none;
  transition: all 250ms var(--tbs-ease);
  box-shadow: var(--tbs-shadow);
}
.tbs-related-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--tbs-shadow-md);
  border-color: var(--tbs-primary-border);
}
.tbs-related-cover {
  width: 100%;
  aspect-ratio: 3/2;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
}
.tbs-related-cover img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 400ms var(--tbs-ease);
}
.tbs-related-card:hover .tbs-related-cover img { transform: scale(1.05); }
.tbs-related-info {
  padding: 14px 16px;
}
.tbs-related-name {
  font-size: 14px;
  font-weight: 700;
  color: var(--tbs-text);
  line-height: 1.3;
  margin-bottom: 4px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}
.tbs-related-author {
  font-size: 12px;
  color: var(--tbs-text-2);
  margin-bottom: 8px;
}
.tbs-related-tag {
  display: inline-block;
  font-size: 11px;
  font-weight: 600;
  color: var(--tbs-primary);
  background: var(--tbs-primary-soft);
  border: 1px solid var(--tbs-primary-border);
  padding: 3px 9px;
  border-radius: var(--tbs-r-pill);
}