:root {
  --bg: #f6f5fb;
  --bg-soft: #eeecf9;
  --bg-elevated: #ffffff;
  --text: #1c1b29;
  --text-muted: #6b6a80;
  --border: #e5e3f0;
  --accent: #4f46e5;
  --accent-text: #ffffff;
  --good: #16a34a;
  --bad: #dc2626;
  --radius: 14px;
  --radius-sm: 9px;
  --shadow: 0 1px 2px rgba(30, 20, 60, 0.04), 0 6px 20px rgba(30, 20, 60, 0.06);
  --shadow-hover: 0 10px 30px rgba(30, 20, 60, 0.12);
  --font-display: "Fraunces", Georgia, serif;
  --font-body: "Inter", -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-family: var(--font-body);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #131320;
    --bg-soft: #1a1a2c;
    --bg-elevated: #1c1c2e;
    --text: #eeeef7;
    --text-muted: #a6a5bd;
    --border: #2c2c42;
    --accent: #9490f0;
    --accent-text: #14141f;
    --good: #4ade80;
    --bad: #f87171;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.2), 0 6px 24px rgba(0, 0, 0, 0.35);
    --shadow-hover: 0 12px 32px rgba(0, 0, 0, 0.45);
  }
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background:
    radial-gradient(1200px 600px at 15% -10%, color-mix(in srgb, var(--accent) 10%, transparent), transparent 60%),
    var(--bg);
  color: var(--text);
  line-height: 1.6;
  transition: background 0.25s ease;
}

a { color: var(--accent); }

h1, h2, h3, .brand { font-family: var(--font-display); letter-spacing: -0.01em; }

header.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 1.5rem;
  background: color-mix(in srgb, var(--bg-elevated) 88%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
  flex-wrap: wrap;
  row-gap: 0.7rem;
}
@media (max-width: 560px) {
  header.site-header { padding: 0.8rem 1rem; }
}

header.site-header .brand {
  display: flex;
  align-items: center;
  gap: 0.55rem;
  font-weight: 600;
  text-decoration: none;
  color: var(--text);
  font-size: 1.15rem;
  white-space: nowrap;
}
.brand-logo { width: 30px; height: 30px; border-radius: 8px; flex-shrink: 0; }

#global-search {
  width: 100%;
  padding: 0.55rem 0.9rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-size: 0.92rem;
  font-family: var(--font-body);
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}
#global-search:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 18%, transparent);
}

#search-results {
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  margin-top: 0.5rem;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-hover);
  max-height: 60vh;
  overflow-y: auto;
  display: none;
}
#search-results.open { display: block; }
#search-results a {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.6rem 0.9rem;
  text-decoration: none;
  color: var(--text);
  border-bottom: 1px solid var(--border);
  font-size: 0.9rem;
}
#search-results a:last-child { border-bottom: none; }
#search-results a:hover { background: var(--bg-soft); }
#search-results small { color: var(--text-muted); display: block; font-weight: 400; }
.result-icon { font-size: 1.1rem; flex-shrink: 0; }
.search-wrap { position: relative; flex: 1; max-width: 440px; }
@media (max-width: 560px) {
  .search-wrap { flex-basis: 100%; max-width: 100%; order: 3; }
}

main.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2rem 1.5rem 5rem;
}
@media (max-width: 560px) {
  main.container { padding: 1.25rem 1rem 3.5rem; }
}

.hero { max-width: 640px; margin-bottom: 2rem; }
.hero h1 { font-size: clamp(1.6rem, 5vw, 2.3rem); font-weight: 600; margin: 0 0 0.6rem; line-height: 1.15; }
.hero-highlight { color: var(--accent); }
.hero p { color: var(--text-muted); font-size: clamp(0.92rem, 2.5vw, 1.05rem); margin: 0; }

.subject-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 1.1rem;
}

.subject-card {
  position: relative;
  display: block;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.4rem 1.4rem 1.6rem;
  text-decoration: none;
  color: var(--text);
  box-shadow: var(--shadow);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
  overflow: hidden;
}
.subject-card::before {
  content: "";
  position: absolute;
  inset: 0 auto auto 0;
  width: 100%;
  height: 4px;
  background: var(--card-accent, var(--accent));
}
.subject-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-hover);
  border-color: color-mix(in srgb, var(--card-accent, var(--accent)) 40%, var(--border));
}
.subject-icon { font-size: 1.8rem; display: block; margin-bottom: 0.6rem; }
.subject-card h3 { margin: 0 0 0.4rem; font-size: 1.15rem; }
.subject-card p { margin: 0 0 0.9rem; color: var(--text-muted); font-size: 0.9rem; }
.card-arrow { font-size: 0.85rem; font-weight: 600; color: var(--card-accent, var(--accent)); }

.subject-heading { display: flex; align-items: center; gap: 0.6rem; margin-bottom: 1.5rem; }
.subject-heading-icon { font-size: 1.8rem; }
.subject-heading h1 { margin: 0; font-size: 1.9rem; }

.layout {
  display: grid;
  grid-template-columns: 260px 1fr;
  gap: 1.5rem;
  align-items: start;
}
@media (max-width: 800px) {
  .layout { grid-template-columns: 1fr; }
}

nav.sidebar {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.6rem;
  position: sticky;
  top: 5rem;
  max-height: calc(100vh - 6rem);
  overflow-y: auto;
}
nav.sidebar a {
  display: block;
  padding: 0.5rem 0.7rem;
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--text-muted);
  font-size: 0.9rem;
  border-left: 3px solid transparent;
  transition: background 0.12s ease, color 0.12s ease;
}
nav.sidebar a:hover { background: var(--bg-soft); color: var(--text); }
nav.sidebar a.active {
  background: color-mix(in srgb, var(--accent) 12%, transparent);
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 500;
}

@media (max-width: 800px) {
  nav.sidebar {
    position: static;
    max-height: none;
    display: flex;
    gap: 0.4rem;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: thin;
  }
  nav.sidebar a {
    flex-shrink: 0;
    white-space: nowrap;
    border: 1px solid var(--border);
    border-left: 1px solid var(--border);
    border-radius: 999px;
    padding: 0.4rem 0.85rem;
  }
  nav.sidebar a.active { border-color: var(--accent); border-left-color: var(--accent); }
}

.topic-panel {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.75rem 2rem;
  box-shadow: var(--shadow);
}
.topic-panel h2 { margin-top: 0; font-size: 1.5rem; }
@media (max-width: 560px) {
  .topic-panel { padding: 1.25rem 1.1rem; }
  .topic-panel h2 { font-size: 1.3rem; }
}

.table-scroll { overflow-x: auto; margin: 1.2em 0; -webkit-overflow-scrolling: touch; }
.table-scroll table { margin: 0; }

.practice-buttons {
  display: flex;
  gap: 0.6rem;
  flex-wrap: wrap;
  margin: 1rem 0 1.75rem;
}

.btn {
  display: inline-block;
  padding: 0.55rem 1.1rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  text-decoration: none;
  font-size: 0.88rem;
  font-weight: 500;
  font-family: var(--font-body);
  cursor: pointer;
  transition: transform 0.12s ease, box-shadow 0.12s ease, background 0.12s ease;
}
.btn:hover { transform: translateY(-1px); box-shadow: var(--shadow); }
.btn.primary { background: var(--accent); color: var(--accent-text); border-color: var(--accent); }
.btn:disabled { opacity: 0.5; cursor: default; transform: none; box-shadow: none; }

.notes-body h3, .notes-body h4 { margin-top: 1.6em; font-family: var(--font-display); }
.notes-body h3:first-child, .notes-body h4:first-child { margin-top: 0; }
.notes-body ul { padding-left: 1.3em; }
.notes-body li { margin-bottom: 0.3em; }
.notes-body strong { color: var(--text); }
.notes-body table { border-collapse: collapse; width: 100%; min-width: 420px; margin: 1.2em 0; font-size: 0.92rem; }
.notes-body th, .notes-body td { border: 1px solid var(--border); padding: 0.55em 0.75em; text-align: left; }
.notes-body th { background: var(--bg-soft); font-family: var(--font-body); font-weight: 600; }
.notes-body tr:nth-child(even) td { background: color-mix(in srgb, var(--bg-soft) 45%, transparent); }

.mode-tabs { display: flex; gap: 0.5rem; margin-bottom: 1.5rem; flex-wrap: wrap; }
.mode-tabs a {
  padding: 0.5rem 1.05rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  text-decoration: none;
  color: var(--text-muted);
  font-size: 0.88rem;
  font-weight: 500;
  transition: background 0.12s ease, color 0.12s ease, border-color 0.12s ease;
}
.mode-tabs a:hover { border-color: var(--accent); color: var(--text); }
.mode-tabs a.active { background: var(--accent); color: var(--accent-text); border-color: var(--accent); }

.flashcard-wrap { perspective: 1400px; margin-bottom: 1.5rem; }
.flashcard {
  position: relative;
  background: linear-gradient(160deg, var(--bg-elevated), color-mix(in srgb, var(--accent) 6%, var(--bg-elevated)));
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  min-height: 240px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 2.5rem 2rem;
  font-size: 1.2rem;
  font-family: var(--font-display);
  cursor: pointer;
  user-select: none;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.flashcard:hover { box-shadow: var(--shadow-hover); transform: translateY(-2px); }
@media (max-width: 560px) {
  .flashcard { min-height: 190px; padding: 1.75rem 1.25rem; font-size: 1.05rem; }
}
.flashcard .label {
  position: absolute;
  top: 0.9rem;
  left: 1.1rem;
  font-size: 0.7rem;
  font-family: var(--font-body);
  color: var(--accent);
  background: color-mix(in srgb, var(--accent) 14%, transparent);
  padding: 0.2rem 0.6rem;
  border-radius: 999px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-weight: 600;
}

.deck-controls, .quiz-controls { display: flex; justify-content: space-between; align-items: center; gap: 1rem; flex-wrap: wrap; }
@media (max-width: 560px) {
  .deck-controls { gap: 0.5rem; }
  .deck-controls .btn { flex: 1 1 auto; text-align: center; padding: 0.6rem 0.5rem; font-size: 0.82rem; }
}
.progress-text { color: var(--text-muted); font-size: 0.88rem; margin-bottom: 0.9rem; }

.progress-bar { height: 6px; border-radius: 999px; background: var(--bg-soft); overflow: hidden; margin-bottom: 0.6rem; }
.progress-bar > div { height: 100%; background: var(--accent); border-radius: 999px; transition: width 0.25s ease; }

.quiz-question { margin-bottom: 1.5rem; }
.quiz-question h3 { margin-bottom: 1.1rem; font-size: 1.25rem; }
.choice {
  display: block;
  width: 100%;
  text-align: left;
  padding: 0.75rem 1rem;
  margin-bottom: 0.55rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  color: var(--text);
  cursor: pointer;
  font-size: 0.95rem;
  font-family: var(--font-body);
  transition: border-color 0.12s ease, background 0.12s ease, transform 0.1s ease;
}
.choice:hover:not(:disabled) { border-color: var(--accent); transform: translateX(2px); }
.choice.correct { border-color: var(--good); background: color-mix(in srgb, var(--good) 15%, var(--bg-elevated)); }
.choice.incorrect { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 15%, var(--bg-elevated)); }
.choice:disabled { cursor: default; }
.explanation { margin-top: 0.7rem; padding: 0.85rem 1rem; background: var(--bg-soft); border-radius: var(--radius-sm); font-size: 0.9rem; color: var(--text-muted); border-left: 3px solid var(--accent); }

.short-answer textarea {
  width: 100%;
  min-height: 150px;
  padding: 0.9rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  color: var(--text);
  font-family: var(--font-body);
  font-size: 0.95rem;
  resize: vertical;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}
.short-answer textarea:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 15%, transparent);
}
.rubric { margin-top: 1.1rem; padding: 1.1rem 1.3rem; background: var(--bg-soft); border-radius: var(--radius); border-left: 3px solid var(--accent); }
.rubric strong { font-family: var(--font-display); }
.rubric ul { margin: 0.5em 0 0; }

.empty-state { color: var(--text-muted); text-align: center; padding: 3rem 1rem; }

.score-summary { text-align: center; padding: 2.5rem 1rem; }
.score-summary .big { font-size: 2.8rem; font-weight: 600; font-family: var(--font-display); color: var(--accent); }

/* ---- homepage dashboard ---- */
.dash { margin-bottom: 2rem; }
.stat-row {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 0.8rem;
  margin-bottom: 1rem;
}
.stat-card {
  display: block;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.9rem 1.1rem;
  text-decoration: none;
  color: var(--text);
  box-shadow: var(--shadow);
  transition: border-color 0.15s ease, transform 0.15s ease;
}
a.stat-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.stat-big { display: block; font-size: 1.7rem; font-weight: 600; font-family: var(--font-display); color: var(--accent); line-height: 1.2; }
.stat-label { color: var(--text-muted); font-size: 0.82rem; }
.dash-actions { display: flex; gap: 0.6rem; flex-wrap: wrap; align-items: center; }
.weak-chips { display: flex; gap: 0.5rem; flex-wrap: wrap; }
.weak-chips a {
  padding: 0.35rem 0.8rem;
  border-radius: 999px;
  border: 1px solid color-mix(in srgb, var(--bad) 45%, var(--border));
  color: var(--bad);
  text-decoration: none;
  font-size: 0.85rem;
  font-weight: 500;
  background: color-mix(in srgb, var(--bad) 7%, transparent);
}
.weak-chips a:hover { background: color-mix(in srgb, var(--bad) 14%, transparent); }
.due-badge {
  position: absolute;
  top: 0.9rem;
  right: 0.9rem;
  background: color-mix(in srgb, var(--card-accent, var(--accent)) 14%, var(--bg-elevated));
  color: var(--card-accent, var(--accent));
  font-size: 0.72rem;
  font-weight: 600;
  padding: 0.15rem 0.55rem;
  border-radius: 999px;
}

/* ---- spaced-repetition rating buttons ---- */
.rating-buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.5rem;
}
.rate {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.05rem;
  padding: 0.6rem 0.3rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  cursor: pointer;
  font-family: var(--font-body);
  font-weight: 600;
  font-size: 0.9rem;
  transition: border-color 0.12s ease, transform 0.1s ease, background 0.12s ease;
}
.rate small { font-weight: 400; font-size: 0.72rem; color: var(--text-muted); }
.rate:hover { border-color: currentColor; transform: translateY(-1px); }
.rate-again { color: var(--bad); }
.rate-hard { color: #d97706; }
.rate-good { color: var(--accent); }
.rate-easy { color: var(--good); }
@media (prefers-color-scheme: dark) {
  .rate-hard { color: #fbbf24; }
}

/* ---- bottom tab bar (mobile only) ---- */
.tabbar {
  display: none;
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  z-index: 20;
  background: color-mix(in srgb, var(--bg-elevated) 94%, transparent);
  backdrop-filter: blur(10px);
  border-top: 1px solid var(--border);
  padding-bottom: env(safe-area-inset-bottom);
}
.tabbar a {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.1rem;
  padding: 0.45rem 0.2rem 0.55rem;
  text-decoration: none;
  color: var(--text-muted);
  font-size: 0.68rem;
  font-weight: 500;
  position: relative;
}
.tabbar a span { font-size: 1.25rem; line-height: 1.2; }
.tabbar a.active { color: var(--accent); }
.tab-badge {
  position: absolute;
  top: 0.2rem;
  right: calc(50% - 1.6rem);
  background: var(--bad);
  color: #fff;
  font-size: 0.62rem;
  font-weight: 700;
  min-width: 1rem;
  text-align: center;
  padding: 0.05rem 0.3rem;
  border-radius: 999px;
}
@media (max-width: 560px) {
  .tabbar { display: flex; }
  main.container { padding-bottom: calc(4.5rem + env(safe-area-inset-bottom)); }
}

/* search result snippets */
.result-snippet { display: block; color: var(--text-muted); font-weight: 400; margin: 0.1rem 0; }
.result-snippet mark, mark {
  background: color-mix(in srgb, var(--accent) 25%, transparent);
  color: inherit;
  border-radius: 3px;
  padding: 0 2px;
}

/* subject/topic context labels on review cards and questions */
.card-context {
  position: absolute;
  top: 0.9rem;
  right: 1.1rem;
  max-width: 55%;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  font-size: 0.72rem;
  font-family: var(--font-body);
  color: var(--text-muted);
}
.card-source { color: var(--text-muted); font-size: 0.82rem; margin: 0 0 0.5rem; }