:root {
  color-scheme: dark;
  --bg: #101211;
  --panel: #181b1a;
  --panel-strong: #202523;
  --text: #f4f7f3;
  --muted: #a7b0aa;
  --line: #303734;
  --teal: #36d6b2;
  --amber: #f2bd4d;
  --rose: #ff6b8a;
  --blue: #72b7ff;
  --green: #8ee66c;
  --shadow: 0 16px 42px rgba(0, 0, 0, 0.34);
  --radius: 8px;
}

* {
  box-sizing: border-box;
}

html {
  min-height: 100%;
  background: var(--bg);
}

body {
  min-height: 100%;
  margin: 0;
  color: var(--text);
  background:
    linear-gradient(180deg, rgba(54, 214, 178, 0.07), transparent 26rem),
    radial-gradient(circle at 90% 4%, rgba(242, 189, 77, 0.08), transparent 22rem),
    var(--bg);
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  letter-spacing: 0;
}

a {
  color: inherit;
  text-decoration: none;
}

button,
input {
  font: inherit;
}

button {
  cursor: pointer;
}

noscript {
  display: block;
  margin: 1rem;
  padding: 1rem;
  border: 1px solid var(--rose);
  border-radius: var(--radius);
  background: rgba(255, 107, 138, 0.12);
}

.app-shell {
  width: min(1120px, calc(100% - 32px));
  margin: 0 auto;
  padding: 28px 0 48px;
}

.study-shell {
  width: min(880px, calc(100% - 28px));
  margin: 0 auto;
  padding: 18px 0 118px;
}

.site-head,
.chapter-head {
  display: grid;
  gap: 16px;
  margin-bottom: 22px;
}

.site-title {
  display: grid;
  gap: 10px;
}

.eyebrow {
  width: fit-content;
  padding: 5px 9px;
  border: 1px solid rgba(54, 214, 178, 0.45);
  border-radius: var(--radius);
  color: var(--teal);
  background: rgba(54, 214, 178, 0.08);
  font-size: 0.88rem;
  font-weight: 800;
}

h1,
h2,
h3,
p {
  margin: 0;
}

h1 {
  font-size: clamp(2rem, 4vw, 4.1rem);
  line-height: 1.02;
  letter-spacing: 0;
}

h2 {
  font-size: 1.35rem;
  line-height: 1.25;
}

h3 {
  font-size: 1.05rem;
}

.lead {
  max-width: 780px;
  color: var(--muted);
  font-size: 1.03rem;
  line-height: 1.65;
}

.summary-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
}

.quick-actions {
  margin-bottom: 16px;
}

.summary-card,
.category-card,
.chapter-panel,
.quick-card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(24, 27, 26, 0.84);
  box-shadow: var(--shadow);
}

.quick-card {
  display: grid;
  gap: 9px;
  padding: 18px;
}

.quick-card strong {
  font-size: 1.24rem;
}

.quick-card span:last-child {
  color: var(--muted);
  line-height: 1.45;
}

.cbt-entry {
  border-color: rgba(114, 183, 255, 0.45);
  background:
    linear-gradient(135deg, rgba(114, 183, 255, 0.13), transparent 45%),
    rgba(24, 27, 26, 0.9);
}

.cbt-entry:hover,
.cbt-entry:focus-visible {
  border-color: var(--blue);
  outline: none;
}

.summary-card {
  padding: 15px;
}

.summary-card strong {
  display: block;
  margin-top: 4px;
  font-size: 1.55rem;
}

.summary-card span,
.chapter-meta,
.card-counter,
.minor {
  color: var(--muted);
  font-size: 0.92rem;
}

.roadmap {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.category-card {
  display: grid;
  gap: 14px;
  padding: 18px;
}

.category-top {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  border-bottom: 1px solid var(--line);
  padding-bottom: 13px;
}

.category-code {
  display: inline-grid;
  place-items: center;
  width: 42px;
  height: 42px;
  border-radius: var(--radius);
  color: var(--bg);
  background: var(--amber);
  font-weight: 900;
}

.chapter-list {
  display: grid;
  gap: 8px;
}

.chapter-link {
  display: grid;
  grid-template-columns: 42px 1fr auto;
  align-items: center;
  gap: 10px;
  min-height: 50px;
  padding: 10px;
  border: 1px solid transparent;
  border-radius: var(--radius);
  background: var(--panel-strong);
  transition: transform 120ms ease, border-color 120ms ease, background 120ms ease;
}

.chapter-link:hover,
.chapter-link:focus-visible {
  transform: translateY(-1px);
  border-color: rgba(54, 214, 178, 0.55);
  outline: none;
}

.chapter-number {
  display: inline-grid;
  place-items: center;
  width: 34px;
  height: 34px;
  border-radius: var(--radius);
  background: #111412;
  color: var(--teal);
  font-weight: 900;
}

.chapter-title {
  font-weight: 800;
  line-height: 1.25;
}

.done-badge {
  min-width: 56px;
  padding: 5px 8px;
  border-radius: var(--radius);
  color: var(--muted);
  background: #111412;
  font-size: 0.82rem;
  font-weight: 800;
  text-align: center;
}

.chapter-link.is-done .done-badge {
  color: var(--bg);
  background: var(--green);
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 4;
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 8px;
  align-items: center;
  padding: 10px 0 14px;
  background: linear-gradient(180deg, var(--bg) 72%, rgba(16, 18, 17, 0));
}

.nav-group {
  display: flex;
  justify-content: center;
  gap: 8px;
}

.nav-btn,
.control-btn,
.complete-toggle {
  min-height: 44px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--panel-strong);
  color: var(--text);
  font-weight: 850;
}

.nav-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 82px;
  padding: 0 12px;
}

.nav-btn:hover,
.control-btn:hover,
.complete-toggle:hover {
  border-color: rgba(54, 214, 178, 0.6);
}

.chapter-panel {
  display: grid;
  gap: 14px;
  padding: 18px;
}

.chapter-title-row {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 16px;
}

.chapter-kicker {
  color: var(--amber);
  font-weight: 900;
}

.complete-toggle {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  width: fit-content;
  padding: 0 12px;
  white-space: nowrap;
}

.complete-toggle input {
  width: 18px;
  height: 18px;
  accent-color: var(--green);
}

.progress-line {
  display: grid;
  gap: 7px;
}

.progress-track {
  height: 10px;
  overflow: hidden;
  border-radius: var(--radius);
  background: #0c0e0d;
}

.progress-fill {
  width: 0%;
  height: 100%;
  border-radius: var(--radius);
  background: linear-gradient(90deg, var(--teal), var(--amber));
  transition: width 180ms ease;
}

.flashcard {
  min-height: 430px;
  display: grid;
  padding: 0;
  border: 1px solid rgba(54, 214, 178, 0.26);
  border-radius: var(--radius);
  background: transparent;
  box-shadow: var(--shadow);
  perspective: 1400px;
  touch-action: pan-y;
}

.flashcard:focus-visible {
  outline: 2px solid var(--teal);
  outline-offset: 3px;
}

.card-inner {
  display: grid;
  min-height: 430px;
  transform-style: preserve-3d;
  transition: transform 360ms cubic-bezier(0.2, 0.7, 0.2, 1);
}

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

.card-face {
  grid-area: 1 / 1;
  display: grid;
  align-content: start;
  gap: 22px;
  min-height: 430px;
  padding: clamp(22px, 4vw, 38px);
  border-radius: var(--radius);
  background:
    linear-gradient(145deg, rgba(54, 214, 178, 0.12), transparent 42%),
    var(--panel);
  backface-visibility: hidden;
  overflow: hidden;
}

.card-back {
  transform: rotateY(180deg);
}

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

.importance {
  color: var(--amber);
  font-size: 1.12rem;
  font-weight: 900;
  white-space: nowrap;
}

.face-label {
  color: var(--teal);
  font-size: 0.92rem;
  font-weight: 900;
}

.front-text {
  display: grid;
  align-items: center;
  min-height: 230px;
  font-size: clamp(1.85rem, 4.6vw, 3.2rem);
  font-weight: 950;
  line-height: 1.18;
  word-break: keep-all;
  overflow-wrap: anywhere;
}

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

.answer-list li {
  display: grid;
  gap: 5px;
  padding: 13px 14px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #111412;
  line-height: 1.55;
  word-break: keep-all;
  overflow-wrap: anywhere;
}

.answer-list b {
  color: var(--amber);
  font-size: 0.92rem;
}

.answer-list span {
  color: var(--text);
  font-size: 1.02rem;
}

.tag-row {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
}

.tag {
  padding: 5px 8px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--muted);
  background: rgba(255, 255, 255, 0.03);
  font-size: 0.82rem;
  font-weight: 800;
}

.study-controls {
  position: fixed;
  left: 50%;
  bottom: 14px;
  z-index: 8;
  display: grid;
  grid-template-columns: 1fr 1.15fr 1fr;
  gap: 8px;
  width: min(840px, calc(100% - 28px));
  transform: translateX(-50%);
  padding: 9px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(24, 27, 26, 0.94);
  box-shadow: var(--shadow);
  backdrop-filter: blur(12px);
}

.control-btn {
  padding: 0 12px;
}

.control-btn.primary {
  color: var(--bg);
  background: var(--teal);
  border-color: transparent;
}

.control-btn:disabled,
.nav-btn.is-disabled {
  opacity: 0.44;
  pointer-events: none;
}

.empty-state {
  padding: 24px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--panel);
}

.cbt-shell {
  width: min(1180px, calc(100% - 28px));
  margin: 0 auto;
  padding: 22px 0 48px;
}

.cbt-header,
.cbt-panel,
.question-card,
.result-card,
.catalog-card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(24, 27, 26, 0.88);
  box-shadow: var(--shadow);
}

.cbt-header {
  display: grid;
  gap: 14px;
  margin-bottom: 14px;
  padding: 18px;
}

.cbt-top {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 16px;
}

.cbt-actions,
.mode-grid,
.cbt-toolbar,
.exam-actions,
.result-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.mode-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.cbt-layout {
  display: grid;
  grid-template-columns: 310px 1fr;
  gap: 14px;
  align-items: start;
}

.cbt-panel,
.catalog-card,
.result-card {
  display: grid;
  gap: 14px;
  padding: 16px;
}

.source-list,
.subject-list {
  display: grid;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.source-list li,
.subject-list li {
  padding: 10px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #111412;
  color: var(--muted);
  line-height: 1.45;
}

.source-list a {
  color: var(--blue);
  font-weight: 800;
}

.cbt-select {
  width: 100%;
  min-height: 44px;
  padding: 0 10px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #111412;
  color: var(--text);
}

.catalog-list {
  display: grid;
  gap: 8px;
  max-height: 560px;
  overflow: auto;
  padding-right: 4px;
}

.question-row {
  display: grid;
  grid-template-columns: 74px 1fr auto;
  gap: 9px;
  align-items: center;
  width: 100%;
  min-height: 54px;
  padding: 9px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--panel-strong);
  color: var(--text);
  text-align: left;
}

.question-row:hover,
.question-row:focus-visible {
  border-color: var(--teal);
  outline: none;
}

.question-row strong {
  color: var(--teal);
}

.question-code {
  display: grid;
  place-items: center;
  min-height: 42px;
  border-radius: var(--radius);
  background: #111412;
  line-height: 1;
}

.question-code span {
  margin-bottom: 3px;
  color: var(--muted);
  font-size: 0.72rem;
  letter-spacing: 0;
}

.question-summary {
  color: var(--muted);
  font-size: 0.88rem;
  line-height: 1.45;
}

.question-summary b {
  display: inline-block;
  margin-right: 7px;
  color: var(--text);
}

.question-summary em {
  display: inline-block;
  margin: 0 0 4px;
  padding: 2px 7px;
  border: 1px solid rgba(54, 214, 178, 0.28);
  border-radius: var(--radius);
  color: var(--teal);
  font-style: normal;
  font-weight: 800;
}

.exam-shell {
  display: grid;
  gap: 14px;
}

.exam-head {
  display: grid;
  gap: 10px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(24, 27, 26, 0.9);
}

.exam-status {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
}

.timer {
  color: var(--amber);
  font-weight: 950;
}

.question-map {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.map-btn {
  width: 36px;
  height: 36px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #111412;
  color: var(--muted);
  font-weight: 900;
}

.map-btn.is-current {
  color: var(--bg);
  background: var(--teal);
}

.map-btn.is-answered {
  border-color: rgba(142, 230, 108, 0.65);
  color: var(--green);
}

.map-btn.is-flagged {
  box-shadow: inset 0 -3px 0 var(--amber);
}

.question-card {
  display: grid;
  gap: 16px;
  padding: clamp(18px, 3vw, 28px);
}

.question-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
}

.question-title {
  font-size: clamp(1.25rem, 3vw, 2rem);
  line-height: 1.35;
  word-break: keep-all;
  overflow-wrap: anywhere;
}

.options-list {
  display: grid;
  gap: 9px;
}

.option-btn {
  display: grid;
  grid-template-columns: 34px 1fr;
  gap: 10px;
  align-items: start;
  width: 100%;
  min-height: 54px;
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #111412;
  color: var(--text);
  text-align: left;
  line-height: 1.45;
}

.option-btn:hover,
.option-btn:focus-visible {
  border-color: var(--teal);
  outline: none;
}

.option-index {
  display: inline-grid;
  place-items: center;
  width: 28px;
  height: 28px;
  border-radius: var(--radius);
  background: var(--panel-strong);
  color: var(--teal);
  font-weight: 950;
}

.option-btn.is-selected {
  border-color: var(--blue);
  background: rgba(114, 183, 255, 0.12);
}

.option-btn.is-correct {
  border-color: var(--green);
  background: rgba(142, 230, 108, 0.12);
}

.option-btn.is-wrong {
  border-color: var(--rose);
  background: rgba(255, 107, 138, 0.12);
}

.explain-box {
  display: grid;
  gap: 7px;
  padding: 13px;
  border: 1px solid rgba(242, 189, 77, 0.42);
  border-radius: var(--radius);
  background: rgba(242, 189, 77, 0.08);
  line-height: 1.55;
}

.score-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
}

.score-box {
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #111412;
}

.score-box strong {
  display: block;
  margin-top: 5px;
  font-size: 1.5rem;
}

.subject-score-table {
  width: 100%;
  border-collapse: collapse;
  overflow: hidden;
  border-radius: var(--radius);
}

.subject-score-table th,
.subject-score-table td {
  padding: 10px;
  border-bottom: 1px solid var(--line);
  background: #111412;
  text-align: left;
}

.subject-score-table th {
  color: var(--amber);
}

@media (max-width: 760px) {
  .app-shell,
  .study-shell {
    width: min(100% - 20px, 680px);
  }

  .app-shell {
    padding-top: 18px;
  }

  .summary-grid,
  .roadmap {
    grid-template-columns: 1fr;
  }

  .mode-grid,
  .cbt-layout,
  .score-grid {
    grid-template-columns: 1fr;
  }

  .cbt-top,
  .exam-status {
    display: grid;
  }

  .question-row {
    grid-template-columns: 64px 1fr;
  }

  .question-row .importance {
    grid-column: 2;
  }

  .category-card,
  .chapter-panel {
    padding: 14px;
  }

  .chapter-link {
    grid-template-columns: 38px 1fr;
  }

  .done-badge {
    grid-column: 2;
    justify-self: start;
  }

  .topbar {
    grid-template-columns: 1fr;
  }

  .nav-group {
    justify-content: stretch;
  }

  .nav-btn {
    flex: 1;
    min-width: 0;
  }

  .chapter-title-row {
    display: grid;
  }

  .flashcard,
  .card-face {
    min-height: 440px;
  }

  .front-text {
    min-height: 250px;
  }

  .study-controls {
    bottom: 10px;
    width: calc(100% - 18px);
  }
}

@media (max-width: 390px) {
  .nav-btn,
  .control-btn {
    padding: 0 8px;
    font-size: 0.92rem;
  }

  .front-text {
    font-size: 1.55rem;
  }
}