/* =========================================================================
   CBSE Prep — Design System
   -------------------------------------------------------------------------
   Concept: "The Marks Margin" — on Indian answer sheets, examiners work in
   a ruled red margin down the side of the page, ticking off marks as they
   go. We reuse that ruled margin as the site's own navigation/progress
   device (see .margin-rule, breadcrumbs, progress ticks), instead of a
   generic progress bar. Fonts: Newsreader (an academic serif, used for
   headings/hero — evokes a textbook, not a cream-and-terracotta template),
   Inter (UI/body), IBM Plex Mono (numbers, marks, roll-no./breadcrumb feel).
   ========================================================================= */

:root {
  /* ---- Color tokens ---- */
  --ink-navy: #1b2a4a;
  --ink-navy-soft: #2c3e63;
  --paper: #f6f5f0;
  --paper-raised: #ffffff;
  --marigold: #e8a33d;
  --marigold-deep: #c9821f;
  --correction-red: #b23a2e;
  --correction-red-soft: #d9887c;
  --success-green: #2f7a5c;
  --slate: #5b6478;
  --slate-light: #8890a0;
  --line: #e1ddd2;
  --line-strong: #c9c3b3;

  /* ---- Type ---- */
  --font-display: "Newsreader", "Source Serif 4", Georgia, serif;
  --font-body: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --font-mono: "IBM Plex Mono", "SFMono-Regular", Consolas, monospace;

  /* ---- Layout ---- */
  --max-width: 1120px;
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --shadow-card: 0 1px 2px rgba(27, 42, 74, 0.06), 0 8px 24px -12px rgba(27, 42, 74, 0.18);
  --shadow-card-hover: 0 4px 10px rgba(27, 42, 74, 0.10), 0 16px 36px -14px rgba(27, 42, 74, 0.28);
  --shadow-flip: 0 20px 40px -16px rgba(27, 42, 74, 0.35);

  --header-h: 64px;
  --transition-fast: 160ms ease;
  --transition-med: 320ms cubic-bezier(0.22, 0.61, 0.36, 1);
}

/* ---- Dark / "Night Study" mode ---- */
[data-theme="night"] {
  --ink-navy: #eef0f6;
  --ink-navy-soft: #c7cde0;
  --paper: #10182c;
  --paper-raised: #182238;
  --marigold: #f0b25a;
  --marigold-deep: #f6c67a;
  --correction-red: #e2685a;
  --correction-red-soft: #a24339;
  --success-green: #59b590;
  --slate: #a9b0c3;
  --slate-light: #7d8398;
  --line: #2a3550;
  --line-strong: #3a4666;
  --shadow-card: 0 1px 2px rgba(0, 0, 0, 0.3), 0 8px 24px -12px rgba(0, 0, 0, 0.6);
  --shadow-card-hover: 0 4px 10px rgba(0, 0, 0, 0.4), 0 16px 36px -14px rgba(0, 0, 0, 0.7);
}

/* ---- Reset ---- */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font-body);
  background: var(--paper);
  color: var(--ink-navy);
  -webkit-font-smoothing: antialiased;
  transition: background var(--transition-med), color var(--transition-med);
}
img { max-width: 100%; display: block; }
a { color: inherit; }
button { font-family: inherit; }
ul { list-style: none; margin: 0; padding: 0; }
h1, h2, h3, h4 { font-family: var(--font-display); margin: 0; font-weight: 600; letter-spacing: -0.01em; }
p { margin: 0; }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.001ms !important; animation-iteration-count: 1 !important; transition-duration: 0.001ms !important; scroll-behavior: auto !important; }
}

:focus-visible {
  outline: 3px solid var(--marigold);
  outline-offset: 2px;
  border-radius: 4px;
}

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

.visually-hidden {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

.skip-link {
  position: absolute; left: 12px; top: -60px; background: var(--marigold);
  color: var(--ink-navy); padding: 10px 16px; border-radius: var(--radius-sm);
  font-weight: 600; z-index: 1000; transition: top var(--transition-fast);
}
.skip-link:focus { top: 12px; }

/* =========================================================================
   Header
   ========================================================================= */
.site-header {
  position: sticky; top: 0; z-index: 100;
  height: var(--header-h);
  display: flex; align-items: center;
  background: var(--paper); /* fallback for browsers without color-mix() support */
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.site-header .container { display: flex; align-items: center; justify-content: space-between; width: 100%; }

.brand {
  display: flex; align-items: center; gap: 10px;
  font-family: var(--font-display); font-weight: 600; font-size: 1.15rem;
  text-decoration: none; color: var(--ink-navy);
}
.brand-mark {
  width: 34px; height: 34px; border-radius: 9px; background: var(--ink-navy);
  display: flex; align-items: center; justify-content: center; flex-shrink: 0;
}
.brand-mark svg { width: 19px; height: 19px; }

.header-actions { display: flex; align-items: center; gap: 10px; }

.icon-btn {
  width: 40px; height: 40px; border-radius: 10px;
  border: 1px solid var(--line); background: var(--paper-raised);
  display: flex; align-items: center; justify-content: center;
  cursor: pointer; color: var(--ink-navy);
  transition: border-color var(--transition-fast), transform var(--transition-fast);
}
.icon-btn:hover { border-color: var(--line-strong); transform: translateY(-1px); }
.icon-btn svg { width: 18px; height: 18px; }

.install-btn {
  display: none;
  align-items: center; gap: 8px;
  padding: 9px 14px; border-radius: 10px; border: none;
  background: var(--marigold); color: var(--ink-navy);
  font-weight: 600; font-size: 0.85rem; cursor: pointer;
  transition: transform var(--transition-fast), background var(--transition-fast);
}
.install-btn.is-visible { display: inline-flex; }
.install-btn:hover { transform: translateY(-1px); background: var(--marigold-deep); }
.install-btn svg { width: 15px; height: 15px; }

/* =========================================================================
   Breadcrumb — doubles as "the marks margin" wayfinder
   ========================================================================= */
.breadcrumb-bar {
  border-bottom: 1px solid var(--line);
  background: var(--paper);
}
.breadcrumb {
  display: flex; align-items: center; flex-wrap: wrap; gap: 6px;
  padding: 14px 0;
  font-family: var(--font-mono); font-size: 0.78rem; letter-spacing: 0.01em;
  color: var(--slate);
}
.breadcrumb a {
  text-decoration: none; color: var(--slate);
  padding: 4px 8px; border-radius: 6px;
  transition: background var(--transition-fast), color var(--transition-fast);
}
.breadcrumb a:hover { background: var(--line); color: var(--ink-navy); }
.breadcrumb .crumb-sep { color: var(--line-strong); }
.breadcrumb .crumb-current { color: var(--ink-navy); font-weight: 600; padding: 4px 8px; }

.back-btn {
  display: inline-flex; align-items: center; gap: 6px;
  border: none; background: none; cursor: pointer;
  font-family: var(--font-mono); font-size: 0.78rem; font-weight: 600;
  color: var(--ink-navy); padding: 6px 0; margin-bottom: 4px;
}
.back-btn svg { width: 14px; height: 14px; }
.back-btn:hover { color: var(--correction-red); }

/* =========================================================================
   Buttons (shared)
   ========================================================================= */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 12px 22px; border-radius: 10px; border: none;
  font-weight: 600; font-size: 0.95rem; cursor: pointer;
  text-decoration: none; transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}
.btn-primary { background: var(--ink-navy); color: var(--paper); }
.btn-primary:hover { transform: translateY(-2px); box-shadow: var(--shadow-card-hover); }
.btn-outline { background: transparent; color: var(--ink-navy); border: 1.5px solid var(--line-strong); }
.btn-outline:hover { border-color: var(--ink-navy); }

/* =========================================================================
   Main / page transition
   ========================================================================= */
#app-main { min-height: calc(100vh - var(--header-h)); }
.view { animation: view-in var(--transition-med) both; }
@keyframes view-in {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

.page-head { padding: 40px 0 28px; }
.page-eyebrow {
  font-family: var(--font-mono); font-size: 0.75rem; letter-spacing: 0.08em;
  text-transform: uppercase; color: var(--marigold-deep); font-weight: 600;
  display: flex; align-items: center; gap: 8px; margin-bottom: 10px;
}
.page-eyebrow::before { content: ""; width: 18px; height: 2px; background: var(--correction-red); display: inline-block; }
.page-title { font-size: clamp(1.7rem, 3.4vw, 2.5rem); }
.page-sub { color: var(--slate); margin-top: 10px; font-size: 1.02rem; max-width: 60ch; }

/* =========================================================================
   Hero (Home)
   ========================================================================= */
.hero {
  padding: 64px 0 40px;
  position: relative;
  overflow: hidden;
}
.hero-grid {
  display: grid; grid-template-columns: 1.1fr 0.9fr; gap: 48px; align-items: center;
}
.hero-eyebrow {
  font-family: var(--font-mono); font-size: 0.78rem; letter-spacing: 0.08em;
  text-transform: uppercase; color: var(--correction-red); font-weight: 600;
  margin-bottom: 18px; display: inline-block;
  border: 1px solid var(--correction-red-soft); padding: 6px 12px; border-radius: 999px;
}
.hero h1 {
  font-size: clamp(2.2rem, 5vw, 3.4rem); line-height: 1.08; margin-bottom: 20px;
}
.hero h1 em { font-style: italic; color: var(--marigold-deep); }
.hero-desc { font-size: 1.08rem; color: var(--slate); max-width: 52ch; margin-bottom: 28px; line-height: 1.6; }
.hero-actions { display: flex; gap: 14px; flex-wrap: wrap; }

.hero-stats { display: flex; gap: 28px; margin-top: 36px; flex-wrap: wrap; }
.hero-stat .num { font-family: var(--font-mono); font-size: 1.5rem; font-weight: 700; color: var(--ink-navy); }
.hero-stat .lbl { font-size: 0.78rem; color: var(--slate); margin-top: 2px; }

/* Exam-paper header panel — the "signature" visual on Home */
.exam-card {
  background: var(--paper-raised);
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  padding: 28px 26px 26px 30px;
  position: relative;
  font-family: var(--font-mono);
}
.exam-card::before {
  content: ""; position: absolute; left: 0; top: 14px; bottom: 14px; width: 3px;
  background: repeating-linear-gradient(to bottom, var(--correction-red) 0 4px, transparent 4px 10px);
  border-radius: 2px;
}
.exam-card-row {
  display: flex; justify-content: space-between; font-size: 0.72rem;
  color: var(--slate); text-transform: uppercase; letter-spacing: 0.06em;
  padding-bottom: 12px; margin-bottom: 14px; border-bottom: 1px dashed var(--line-strong);
}
.exam-card h3 {
  font-family: var(--font-display); font-size: 1.3rem; margin-bottom: 14px; color: var(--ink-navy);
}
.exam-card-list { display: flex; flex-direction: column; gap: 10px; }
.exam-card-list li {
  display: flex; align-items: center; gap: 10px; font-size: 0.85rem; color: var(--ink-navy-soft);
}
.exam-tick {
  width: 20px; height: 20px; border-radius: 50%; border: 1.5px solid var(--success-green);
  color: var(--success-green); display: flex; align-items: center; justify-content: center;
  font-size: 0.65rem; flex-shrink: 0;
}
.exam-card-footer {
  margin-top: 18px; padding-top: 14px; border-top: 1px dashed var(--line-strong);
  display: flex; justify-content: space-between; font-size: 0.72rem; color: var(--slate);
}
.exam-card-footer strong { color: var(--marigold-deep); }

/* =========================================================================
   Class cards (Home)
   ========================================================================= */
.section { padding: 30px 0 64px; }
.section-title-row { display: flex; align-items: baseline; justify-content: space-between; margin-bottom: 22px; flex-wrap: wrap; gap: 8px; }
.section-title { font-size: 1.5rem; }
.section-note { font-size: 0.85rem; color: var(--slate); font-family: var(--font-mono); }

.class-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }

.class-card {
  position: relative;
  background: var(--paper-raised);
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  padding: 30px 24px 26px;
  text-decoration: none; color: var(--ink-navy);
  box-shadow: var(--shadow-card);
  overflow: hidden;
  transition: transform var(--transition-med), box-shadow var(--transition-med), border-color var(--transition-med);
}
.class-card:hover, .class-card:focus-visible { transform: translateY(-6px); box-shadow: var(--shadow-card-hover); border-color: var(--line-strong); }
.class-card::after {
  content: ""; position: absolute; left: 0; top: 0; bottom: 0; width: 4px;
  background: var(--class-accent, var(--marigold));
  transition: width var(--transition-med);
}
.class-card:hover::after { width: 7px; }
.class-card .class-num {
  font-family: var(--font-mono); font-size: 0.75rem; color: var(--slate); letter-spacing: 0.06em;
}
.class-card h3 { font-size: 1.75rem; margin: 6px 0 10px; }
.class-card p { color: var(--slate); font-size: 0.92rem; line-height: 1.5; }
.class-card .class-cta {
  margin-top: 18px; display: flex; align-items: center; gap: 6px;
  font-size: 0.85rem; font-weight: 600; color: var(--class-accent, var(--marigold-deep));
}
.class-card .class-cta svg { width: 14px; height: 14px; transition: transform var(--transition-fast); }
.class-card:hover .class-cta svg { transform: translateX(3px); }

/* =========================================================================
   Card grids (Subjects / Resource types)
   ========================================================================= */
.card-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 18px; }

.subject-card, .resource-card {
  background: var(--paper-raised);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  padding: 22px 20px;
  text-decoration: none; color: var(--ink-navy);
  box-shadow: var(--shadow-card);
  display: flex; flex-direction: column; gap: 12px;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast), border-color var(--transition-fast);
}
.subject-card:hover, .resource-card:hover, .subject-card:focus-visible, .resource-card:focus-visible {
  transform: translateY(-4px); box-shadow: var(--shadow-card-hover); border-color: var(--line-strong);
}
.card-icon {
  width: 44px; height: 44px; border-radius: 10px; background: var(--paper);
  border: 1px solid var(--line);
  display: flex; align-items: center; justify-content: center; color: var(--marigold-deep);
}
.card-icon svg { width: 22px; height: 22px; }
.subject-card h3, .resource-card h3 { font-size: 1.1rem; font-family: var(--font-body); font-weight: 700; }
.subject-card .meta { font-family: var(--font-mono); font-size: 0.74rem; color: var(--slate); }
.resource-card p { font-size: 0.86rem; color: var(--slate); line-height: 1.5; }

.resource-card { padding: 28px 24px; }
.resource-card .card-icon { width: 52px; height: 52px; }
.resource-card .card-icon svg { width: 26px; height: 26px; }

/* Chapter list */
.chapter-list { display: flex; flex-direction: column; gap: 10px; }
.chapter-item {
  display: flex; align-items: center; gap: 16px;
  background: var(--paper-raised); border: 1px solid var(--line); border-radius: var(--radius-md);
  padding: 16px 18px; text-decoration: none; color: var(--ink-navy);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast), border-color var(--transition-fast);
}
.chapter-item:hover, .chapter-item:focus-visible { transform: translateX(4px); box-shadow: var(--shadow-card); border-color: var(--line-strong); }
.chapter-num {
  font-family: var(--font-mono); font-weight: 700; font-size: 0.95rem;
  width: 40px; height: 40px; border-radius: 10px; flex-shrink: 0;
  background: var(--paper); border: 1px solid var(--line);
  display: flex; align-items: center; justify-content: center; color: var(--marigold-deep);
}
.chapter-item h3 { font-size: 1.02rem; font-family: var(--font-body); font-weight: 600; }
.chapter-item .chev { margin-left: auto; color: var(--slate-light); width: 16px; height: 16px; flex-shrink: 0; }

/* =========================================================================
   Skeleton loaders
   ========================================================================= */
.skeleton { position: relative; overflow: hidden; background: var(--line); border-radius: var(--radius-md); }
.skeleton::after {
  content: ""; position: absolute; inset: 0; transform: translateX(-100%);
  background: linear-gradient(90deg, transparent, var(--paper-raised), transparent); /* fallback */
  background: linear-gradient(90deg, transparent, color-mix(in srgb, var(--paper-raised) 70%, transparent), transparent);
  animation: shimmer 1.3s infinite;
}
@keyframes shimmer { 100% { transform: translateX(100%); } }
.skeleton-card { height: 150px; }
.skeleton-line { height: 14px; margin-bottom: 10px; }
.skeleton-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 18px; }

/* =========================================================================
   Content areas (protected)
   ========================================================================= */
.content-shell { position: relative; }
.content-protected {
  user-select: none;
  -webkit-user-select: none;
  position: relative;
}
.content-protected img { -webkit-user-drag: none; user-drag: none; pointer-events: none; }

.watermark-layer {
  position: absolute; inset: 0; pointer-events: none; z-index: 1;
  opacity: 0.05;
  background-image: var(--watermark-svg);
  background-repeat: repeat;
  background-size: 260px 160px;
  mix-blend-mode: multiply;
}
[data-theme="night"] .watermark-layer { mix-blend-mode: screen; opacity: 0.06; }

.toast {
  position: fixed; left: 50%; bottom: 28px; transform: translate(-50%, 20px);
  background: var(--ink-navy); color: var(--paper);
  padding: 12px 20px; border-radius: 10px; font-size: 0.88rem;
  box-shadow: var(--shadow-card-hover); z-index: 1000;
  opacity: 0; transition: opacity var(--transition-fast), transform var(--transition-fast);
  pointer-events: none; display: flex; align-items: center; gap: 8px;
}
.toast svg { width: 15px; height: 15px; color: var(--correction-red-soft); flex-shrink: 0; }
.toast.is-visible { opacity: 1; transform: translate(-50%, 0); }

/* Reading layout for summary/notes */
.reading-layout { display: grid; grid-template-columns: 220px 1fr; gap: 40px; align-items: start; }
.toc {
  position: sticky; top: calc(var(--header-h) + 24px);
  background: var(--paper-raised); border: 1px solid var(--line); border-radius: var(--radius-md);
  padding: 18px; font-size: 0.85rem;
}
.toc h4 { font-family: var(--font-mono); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--slate); margin-bottom: 10px; }
.toc ul { display: flex; flex-direction: column; gap: 8px; }
.toc a { text-decoration: none; color: var(--ink-navy-soft); display: block; padding: 3px 0; border-left: 2px solid transparent; padding-left: 10px; transition: border-color var(--transition-fast), color var(--transition-fast); }
.toc a:hover, .toc a.active { border-left-color: var(--marigold); color: var(--ink-navy); font-weight: 600; }
.toc .toc-sub { padding-left: 20px; font-size: 0.92em; }

.prose {
  font-size: 1.04rem; line-height: 1.8; max-width: 74ch;
}
.prose h1, .prose h2, .prose h3 { margin-top: 1.6em; margin-bottom: 0.6em; color: var(--ink-navy); scroll-margin-top: calc(var(--header-h) + 20px); }
.prose h1 { font-size: 1.7rem; border-bottom: 1px solid var(--line); padding-bottom: 0.4em; }
.prose h2 { font-size: 1.35rem; }
.prose h3 { font-size: 1.12rem; font-family: var(--font-body); font-weight: 700; }
.prose p { margin: 0.9em 0; color: var(--ink-navy-soft); }
.prose ul, .prose ol { margin: 0.9em 0; padding-left: 1.4em; color: var(--ink-navy-soft); }
.prose li { margin: 0.35em 0; }
.prose strong { color: var(--ink-navy); }
.prose table { border-collapse: collapse; width: 100%; margin: 1.2em 0; font-size: 0.95rem; }
.prose th, .prose td { border: 1px solid var(--line-strong); padding: 8px 12px; text-align: left; }
.prose th { background: var(--paper); font-family: var(--font-mono); font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.04em; }
.prose blockquote { border-left: 3px solid var(--marigold); margin: 1.2em 0; padding: 0.4em 1em; color: var(--slate); background: var(--paper); border-radius: 0 8px 8px 0; }
.prose code { font-family: var(--font-mono); background: var(--paper); padding: 0.15em 0.4em; border-radius: 4px; font-size: 0.9em; }

/* =========================================================================
   Flip cards (Top 25 Q&A)
   ========================================================================= */
.qna-toolbar { display: flex; align-items: center; justify-content: space-between; gap: 16px; margin-bottom: 26px; flex-wrap: wrap; }
.qna-progress { font-family: var(--font-mono); font-size: 0.82rem; color: var(--slate); display: flex; align-items: center; gap: 10px; }
.qna-progress-track { width: 120px; height: 6px; background: var(--line); border-radius: 999px; overflow: hidden; }
.qna-progress-fill { height: 100%; background: var(--success-green); border-radius: 999px; transition: width var(--transition-med); }
.qna-actions { display: flex; gap: 10px; }

.flip-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(270px, 1fr)); gap: 22px; perspective: 1400px; }

.flip-card {
  height: 210px; cursor: pointer; outline-offset: 4px;
}
.flip-card-inner {
  position: relative; width: 100%; height: 100%;
  transition: transform 0.46s cubic-bezier(0.22, 0.61, 0.36, 1);
  transform-style: preserve-3d;
}
.flip-card.is-flipped .flip-card-inner { transform: rotateY(180deg); }
.flip-card-face {
  position: absolute; inset: 0; backface-visibility: hidden;
  border-radius: var(--radius-md); padding: 20px;
  display: flex; flex-direction: column;
  border: 1px solid var(--line); box-shadow: var(--shadow-card);
  overflow: hidden;
}
.flip-card-front { background: var(--paper-raised); }
.flip-card-back { background: var(--ink-navy); color: var(--paper); transform: rotateY(180deg); }
.flip-card:hover .flip-card-face, .flip-card:focus-visible .flip-card-face { box-shadow: var(--shadow-flip); }

.flip-qnum {
  font-family: var(--font-mono); font-size: 0.72rem; color: var(--marigold-deep);
  font-weight: 700; letter-spacing: 0.04em; margin-bottom: 10px;
}
.flip-card-back .flip-qnum { color: var(--marigold); }
.flip-card-front p { font-size: 0.98rem; font-weight: 600; line-height: 1.5; color: var(--ink-navy); overflow-y: auto; }
.flip-card-back .answer-body { font-size: 0.88rem; line-height: 1.55; overflow-y: auto; color: var(--paper); opacity: 0.94; }
.flip-card-back .answer-body p { margin: 0.5em 0; }
.flip-hint { margin-top: auto; padding-top: 10px; font-family: var(--font-mono); font-size: 0.68rem; color: var(--slate-light); display: flex; align-items: center; gap: 6px; }
.flip-hint svg { width: 12px; height: 12px; }
.flip-card-back .reviewed-stamp {
  margin-left: auto; margin-top: 8px; width: 26px; height: 26px; border-radius: 50%;
  border: 1.5px solid var(--marigold); color: var(--marigold); display: flex; align-items: center; justify-content: center; flex-shrink: 0;
}

/* Study mode overlay */
.study-overlay {
  position: fixed; inset: 0;
  background: var(--ink-navy); /* fallback */
  background: color-mix(in srgb, var(--ink-navy) 92%, transparent);
  z-index: 500; display: flex; flex-direction: column; align-items: center; justify-content: center;
  padding: 24px; backdrop-filter: blur(4px);
}
.study-close { position: absolute; top: 20px; right: 20px; }
.study-progress-label { color: var(--paper); font-family: var(--font-mono); font-size: 0.85rem; margin-bottom: 18px; opacity: 0.8; }
.study-card-wrap { width: min(560px, 92vw); perspective: 1600px; }
.study-card-wrap .flip-card { height: 320px; }
.study-nav { display: flex; align-items: center; gap: 18px; margin-top: 26px; }
.study-nav .icon-btn { background: var(--paper-raised); }
/* .btn-outline normally sits on the page background, so its text uses
   --ink-navy. Here it sits on the dark Study Mode overlay (built from that
   same --ink-navy variable), which made the label invisible — override
   both colors so they contrast with the overlay instead. */
.study-nav .btn-outline {
  color: var(--paper);
  border-color: var(--paper);
  background: transparent;
}
.study-nav .btn-outline:hover {
  color: var(--marigold);
  border-color: var(--marigold);
}

/* =========================================================================
   Mock paper
   ========================================================================= */
.exam-meta-bar {
  display: flex; flex-wrap: wrap; gap: 24px; justify-content: space-between;
  background: var(--paper-raised); border: 1px solid var(--line); border-radius: var(--radius-md);
  padding: 18px 22px; margin-bottom: 20px; font-family: var(--font-mono); font-size: 0.85rem;
}
.exam-meta-bar div span { display: block; font-size: 0.68rem; color: var(--slate); text-transform: uppercase; letter-spacing: 0.06em; margin-bottom: 4px; }
.exam-instructions {
  background: var(--paper); border: 1px dashed var(--line-strong); border-radius: var(--radius-md);
  padding: 18px 22px; margin-bottom: 26px;
}
.exam-instructions h4 { font-family: var(--font-mono); font-size: 0.75rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--slate); margin-bottom: 10px; }
.exam-section { margin-bottom: 32px; }
.exam-section-head { display: flex; align-items: center; gap: 12px; margin-bottom: 14px; }
.exam-section-head h3 { font-size: 1.15rem; }
.marks-badge {
  font-family: var(--font-mono); font-size: 0.72rem; font-weight: 700; color: var(--correction-red);
  border: 1px solid var(--correction-red-soft); padding: 3px 10px; border-radius: 999px;
}
.exam-section .prose { max-width: none; }

.answer-key-toggle {
  display: inline-flex; align-items: center; gap: 8px; margin: 8px 0 18px;
}
.answer-key-panel {
  border: 1px solid var(--line-strong); border-radius: var(--radius-md); background: var(--paper-raised);
  overflow: hidden; max-height: 0; transition: max-height var(--transition-med);
}
.answer-key-panel.is-open { max-height: 6000px; }
.answer-key-inner { padding: 22px 24px; }

/* =========================================================================
   Empty / coming soon / error states
   ========================================================================= */
.empty-state {
  text-align: center; padding: 70px 24px; max-width: 460px; margin: 0 auto;
}
.empty-state .card-icon { margin: 0 auto 18px; width: 56px; height: 56px; }
.empty-state h3 { font-size: 1.3rem; margin-bottom: 10px; }
.empty-state p { color: var(--slate); line-height: 1.6; }

/* =========================================================================
   Footer
   ========================================================================= */
.site-footer { border-top: 1px solid var(--line); padding: 36px 0; margin-top: 40px; }
.footer-grid { display: flex; justify-content: space-between; align-items: flex-start; gap: 24px; flex-wrap: wrap; }
.footer-brand { font-family: var(--font-display); font-weight: 600; }
.footer-note { color: var(--slate); font-size: 0.85rem; max-width: 46ch; line-height: 1.6; margin-top: 8px; }
.footer-meta { font-family: var(--font-mono); font-size: 0.76rem; color: var(--slate-light); text-align: right; }

/* =========================================================================
   Responsive
   ========================================================================= */
@media (max-width: 900px) {
  .hero-grid { grid-template-columns: 1fr; }
  .reading-layout { grid-template-columns: 1fr; }
  .toc { position: static; margin-bottom: 20px; }
  .class-grid { grid-template-columns: 1fr; }
}
@media (max-width: 620px) {
  .container { padding: 0 18px; }
  .hero { padding: 40px 0 24px; }
  .hero-actions { flex-direction: column; align-items: stretch; }
  .exam-meta-bar { flex-direction: column; gap: 12px; }
  .footer-grid { flex-direction: column; }
  .footer-meta { text-align: left; }
  .flip-grid { grid-template-columns: 1fr; }
}