:root {
  color-scheme: light;
  --bg: #f4f6fb;
  --card: #ffffff;
  --ink: #1b1f2a;
  --muted: #5a6372;
  --accent: #3a6bff;
  --accent-2: #00c2ff;
  --accent-soft: rgba(58, 107, 255, 0.12);
  --border: #e2e6ef;
  --shadow: 0 14px 34px rgba(18, 24, 45, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Pretendard", "Noto Sans KR", system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.7;
}

body.theme-dark {
  --bg: #0f1424;
  --card: #151b2e;
  --ink: #f5f7ff;
  --muted: #a9b4d1;
  --border: rgba(255, 255, 255, 0.12);
  --accent-soft: rgba(90, 136, 255, 0.2);
  background: var(--bg);
  color: var(--ink);
}

body.theme-dark .hero {
  background: radial-gradient(circle at top left, rgba(255, 255, 255, 0.12), transparent 40%),
    linear-gradient(135deg, #0f1934, #233a8b 60%, #2563ff);
}

body.theme-dark .toc,
body.theme-dark .unit,
body.theme-dark .toolbar,
body.theme-dark .dashboard__card,
body.theme-dark .quiz-card,
body.theme-dark .playground__panel,
body.theme-dark .side-card {
  background: rgba(21, 27, 46, 0.95);
}

body.focus-mode .toc {
  display: none;
}

.progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 6px;
  background: rgba(255, 255, 255, 0.6);
  z-index: 50;
}

.progress__bar {
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transition: width 0.2s ease;
}

.hero {
  background: radial-gradient(circle at top left, rgba(255, 255, 255, 0.2), transparent 45%),
    linear-gradient(135deg, #1b2a4e, #2f6bff 60%, #00c2ff);
  color: #fff;
  padding: 84px 20px 72px;
}

.hero__content {
  max-width: 1040px;
  margin: 0 auto;
}

.hero__eyebrow {
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  opacity: 0.85;
  margin-bottom: 12px;
}

.hero__subtitle {
  max-width: 760px;
  font-size: 1.05rem;
}

.hero__meta {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 24px;
  font-size: 0.98rem;
  opacity: 0.9;
}

.hero__cta {
  margin-top: 28px;
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.pill {
  border: none;
  padding: 10px 18px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.16);
  color: #fff;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s ease, background 0.2s ease;
}

.pill:hover,
.pill.is-active {
  background: rgba(255, 255, 255, 0.32);
  transform: translateY(-2px);
}

.toolbar {
  max-width: 1040px;
  margin: -28px auto 24px;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(10px);
  border: 1px solid var(--border);
  border-radius: 18px;
  padding: 18px 20px;
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  justify-content: space-between;
  box-shadow: var(--shadow);
}

.toolbar,
.dashboard__card,
.quiz-card,
.unit,
.playground__panel,
.side-card {
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.dashboard__card:hover,
.quiz-card:hover,
.playground__panel:hover,
.side-card:hover {
  transform: translateY(-2px);
  box-shadow: 0 18px 40px rgba(18, 24, 45, 0.12);
}

.toolbar__group {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
}

.search {
  display: flex;
  align-items: center;
  gap: 8px;
  background: var(--bg);
  border-radius: 999px;
  padding: 8px 14px;
  border: 1px solid var(--border);
}

.search input {
  border: none;
  background: transparent;
  outline: none;
  min-width: 220px;
  font-size: 0.95rem;
}

.toolbar__stats {
  color: var(--muted);
  font-size: 0.92rem;
  display: flex;
  gap: 12px;
}

.btn {
  border: 1px solid var(--border);
  background: #fff;
  padding: 8px 14px;
  border-radius: 12px;
  cursor: pointer;
  font-weight: 600;
  transition: all 0.2s ease;
}

.btn:hover {
  border-color: var(--accent);
  color: var(--accent);
  box-shadow: 0 8px 18px rgba(47, 107, 255, 0.12);
}

.btn:focus-visible,
.pill:focus-visible,
.tab:focus-visible,
.search input:focus-visible,
.blank-input input:focus-visible,
.goal-input input:focus-visible,
.note-card textarea:focus-visible {
  outline: 3px solid rgba(58, 107, 255, 0.35);
  outline-offset: 2px;
}

.btn--ghost {
  background: transparent;
  border-style: dashed;
  border-color: var(--accent);
  color: var(--accent);
}

.btn--option {
  width: 100%;
  text-align: left;
  padding: 12px 16px;
}

.btn--success {
  background: rgba(46, 196, 135, 0.12);
  border-color: rgba(46, 196, 135, 0.4);
  color: #1a7f52;
}

.btn--danger {
  background: rgba(255, 99, 71, 0.12);
  border-color: rgba(255, 99, 71, 0.4);
  color: #b42520;
}

.dashboard {
  max-width: 1040px;
  margin: 0 auto 32px;
  padding: 0 20px;
  display: grid;
  gap: 20px;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
}

.dashboard__card,
.quiz-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 22px 24px;
  box-shadow: var(--shadow);
}

.dashboard__hint {
  margin-top: 6px;
  color: var(--muted);
  font-size: 0.95rem;
}

.dashboard__stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 12px;
  margin: 18px 0;
}

.stat__label {
  display: block;
  color: var(--muted);
  font-size: 0.85rem;
}

.dashboard__bar {
  height: 10px;
  background: rgba(47, 107, 255, 0.12);
  border-radius: 999px;
  overflow: hidden;
}

.dashboard__bar-fill {
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transition: width 0.3s ease;
}

.dashboard__actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 18px;
}

.quiz-card__label {
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  font-weight: 700;
  font-size: 0.85rem;
}

.quiz-card__answer {
  margin-top: 12px;
  padding: 12px 14px;
  background: var(--accent-soft);
  border-radius: 12px;
  opacity: 0;
  max-height: 0;
  overflow: hidden;
  transition: opacity 0.2s ease, max-height 0.2s ease;
}

.quiz-card__answer.is-visible {
  opacity: 1;
  max-height: 120px;
}

.playground {
  max-width: 1040px;
  margin: 0 auto 40px;
  padding: 0 20px;
}

.playground__intro {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 18px;
}

.playground__intro h2 {
  margin: 0 0 8px;
}

.playground__controls {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.playground__grid {
  display: grid;
  grid-template-columns: minmax(0, 2fr) minmax(0, 1fr);
  gap: 20px;
}

.playground__panel,
.side-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 18px;
  padding: 20px;
  box-shadow: var(--shadow);
}

.combo-meter {
  display: flex;
  align-items: center;
  gap: 12px;
  justify-content: space-between;
  margin-bottom: 16px;
  font-weight: 600;
}

.combo-meter__track {
  flex: 1;
  height: 10px;
  border-radius: 999px;
  background: rgba(58, 107, 255, 0.15);
  overflow: hidden;
}

.combo-meter__fill {
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transition: width 0.3s ease;
}

.tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 16px;
}

.tab {
  border: 1px solid var(--border);
  padding: 8px 14px;
  border-radius: 999px;
  background: var(--bg);
  cursor: pointer;
  font-weight: 600;
}

.tab.is-active {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent);
}

.tab-panel {
  display: none;
}

.tab-panel.is-active {
  display: block;
}

.quiz-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  color: var(--muted);
  font-size: 0.9rem;
  margin-bottom: 12px;
}

.option-grid {
  display: grid;
  gap: 10px;
  margin: 16px 0;
}

.quiz-actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.quiz-feedback {
  margin-top: 12px;
  color: var(--muted);
}

.blank-input {
  display: flex;
  flex-direction: column;
  gap: 6px;
  margin: 16px 0;
  font-weight: 600;
}

.blank-input input {
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--bg);
  font-size: 0.95rem;
}

.flashcard {
  perspective: 1200px;
  position: relative;
  height: 220px;
  cursor: pointer;
}

.flashcard__front,
.flashcard__back {
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba(58, 107, 255, 0.14), rgba(0, 194, 255, 0.12));
  border-radius: 18px;
  padding: 20px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  backface-visibility: hidden;
  transition: transform 0.6s ease;
}

.flashcard__back {
  transform: rotateY(180deg);
}

.flashcard.is-flipped .flashcard__front {
  transform: rotateY(180deg);
}

.flashcard.is-flipped .flashcard__back {
  transform: rotateY(360deg);
}

.flashcard__label {
  font-size: 0.82rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 8px;
}

.mission-list {
  list-style: none;
  padding: 0;
  margin: 16px 0;
  display: grid;
  gap: 12px;
}

.mission-list li {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  align-items: center;
  font-size: 0.95rem;
}

.mission-btn.is-complete {
  border-color: rgba(46, 196, 135, 0.5);
  color: #1a7f52;
}

.badge-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: 10px;
}

.badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 10px 12px;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--bg);
  font-weight: 600;
  color: var(--muted);
}

.badge.is-earned {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent);
}

.badge-hint,
.mission-feedback {
  margin-top: 12px;
  color: var(--muted);
  font-size: 0.9rem;
}

.goal-input {
  display: flex;
  flex-direction: column;
  gap: 6px;
  margin: 12px 0;
  font-weight: 600;
}

.goal-input input,
.note-card textarea {
  padding: 8px 10px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--bg);
}

.goal-progress {
  height: 10px;
  background: rgba(58, 107, 255, 0.12);
  border-radius: 999px;
  overflow: hidden;
}

.goal-progress__fill {
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transition: width 0.3s ease;
}

.goal-meta {
  margin-top: 10px;
  color: var(--muted);
  font-size: 0.9rem;
}

.timer-display {
  font-size: 2.2rem;
  font-weight: 700;
  margin: 10px 0;
  letter-spacing: 0.08em;
}

.timer-presets {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 12px;
}

.timer-hint {
  margin-top: 12px;
  color: var(--muted);
  font-size: 0.9rem;
}

.history-list {
  padding-left: 18px;
  margin: 12px 0 0;
  display: grid;
  gap: 6px;
  color: var(--muted);
  font-size: 0.9rem;
}

.note-card textarea {
  width: 100%;
  min-height: 120px;
  resize: vertical;
  font-size: 0.95rem;
}

.note-status {
  margin-top: 10px;
  color: var(--muted);
  font-size: 0.9rem;
}

.routine-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 8px;
}

.routine-hint,
.routine-status {
  color: var(--muted);
  font-size: 0.9rem;
  margin: 8px 0 12px;
}

.routine-btn.is-complete {
  border-color: rgba(46, 196, 135, 0.5);
  color: #1a7f52;
}

.pop-quiz {
  position: fixed;
  inset: 0;
  background: rgba(13, 18, 30, 0.6);
  display: none;
  align-items: center;
  justify-content: center;
  z-index: 80;
  padding: 20px;
}

.pop-quiz.is-active {
  display: flex;
}

.pop-quiz__card {
  background: var(--card);
  border-radius: 20px;
  padding: 24px;
  max-width: 520px;
  width: 100%;
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
}

.pop-quiz__header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.pop-quiz__meta {
  color: var(--muted);
  font-size: 0.92rem;
}

@media (max-width: 980px) {
  .playground__grid {
    grid-template-columns: 1fr;
  }
}

.toc {
  max-width: 1040px;
  margin: 0 auto 40px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 24px 28px;
  box-shadow: var(--shadow);
}

.toc h2 {
  margin-top: 0;
}

.toc ol {
  margin: 0;
  padding-left: 20px;
  display: grid;
  gap: 6px;
}

.toc a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 600;
}

main {
  max-width: 1040px;
  margin: 0 auto 80px;
  padding: 0 20px;
}

.unit {
  margin-bottom: 32px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 20px;
  box-shadow: var(--shadow);
  overflow: hidden;
}

.unit__shell {
  padding: 0 28px 28px;
}

.unit__header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 12px;
  padding: 28px 0 12px;
  cursor: pointer;
  list-style: none;
}

.unit__header::-webkit-details-marker {
  display: none;
}

.unit__header h2 {
  margin: 0 0 4px;
}

.unit__badge {
  background: var(--accent-soft);
  color: var(--accent);
  padding: 8px 12px;
  border-radius: 12px;
  font-weight: 700;
  white-space: nowrap;
}

.concept-block,
.question-block {
  padding: 20px 0;
  border-top: 1px dashed var(--border);
}

.concept-block:first-of-type,
.question-block:first-of-type {
  border-top: none;
}

.concept-block h3,
.question-block h3 {
  margin-bottom: 12px;
  color: #1f2c4d;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 12px;
  font-size: 0.95rem;
}

th,
td {
  border: 1px solid var(--border);
  padding: 10px 12px;
  text-align: left;
}

th {
  background: #f0f4ff;
}

.checklist,
.example {
  background: var(--accent-soft);
  border-radius: 12px;
  padding: 16px;
  margin-top: 16px;
}

.question-block ol {
  padding-left: 20px;
}

.question-block ul {
  padding-left: 20px;
  margin-top: 8px;
}

.answer {
  margin-top: 6px;
  font-weight: 700;
  color: var(--accent);
  opacity: 0;
  max-height: 0;
  overflow: hidden;
  transition: opacity 0.2s ease, max-height 0.2s ease;
}

body.show-answers .answer {
  opacity: 1;
  max-height: 80px;
}

.footer {
  text-align: center;
  padding: 40px 20px 60px;
  color: var(--muted);
}

@media (max-width: 860px) {
  .hero {
    padding: 64px 16px 52px;
  }

  .toolbar {
    margin: -24px 16px 24px;
  }

  .toc,
  main {
    margin-left: 16px;
    margin-right: 16px;
  }

  .unit__shell {
    padding: 0 20px 24px;
  }
}

@media (max-width: 600px) {
  .search input {
    min-width: 160px;
  }

  .unit__header {
    flex-direction: column;
    align-items: flex-start;
  }
}