:root {
  color-scheme: light;
  --bg: #f6f8f7;
  --surface: #ffffff;
  --surface-soft: #edf5f1;
  --ink: #162622;
  --muted: #65736d;
  --line: #dce5e0;
  --teal: #1c7c68;
  --teal-dark: #135c4d;
  --amber: #c98222;
  --red: #b9413b;
  --green: #1f7a4a;
  --shadow: 0 18px 45px rgba(24, 57, 48, 0.1);
  font-family:
    "Noto Sans SC",
    "PingFang SC",
    "Microsoft YaHei",
    system-ui,
    -apple-system,
    BlinkMacSystemFont,
    sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  margin: 0;
  background: var(--bg);
  color: var(--ink);
}

button,
a {
  font: inherit;
}

button {
  cursor: pointer;
}

button:focus-visible,
a:focus-visible {
  outline: 3px solid rgba(28, 124, 104, 0.28);
  outline-offset: 3px;
}

.app-shell {
  display: grid;
  grid-template-columns: 240px minmax(0, 1fr) 320px;
  gap: 24px;
  width: min(1440px, 100%);
  min-height: 100vh;
  margin: 0 auto;
  padding: 24px;
}

.rail,
.quiz-panel,
.study-panel {
  min-width: 0;
}

.rail {
  display: flex;
  flex-direction: column;
  gap: 28px;
  border-right: 1px solid var(--line);
  padding: 8px 24px 8px 0;
}

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

.brand-mark {
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  border-radius: 8px;
  background: var(--ink);
  color: #ffffff;
  font-size: 22px;
  font-weight: 800;
}

.brand h1 {
  margin: 0;
  font-size: 22px;
  line-height: 1.2;
}

.brand p {
  margin: 4px 0 0;
  color: var(--muted);
  font-size: 13px;
}

.mode-nav {
  display: grid;
  gap: 8px;
}

.mode-button {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 44px;
  border: 1px solid transparent;
  border-radius: 8px;
  background: transparent;
  color: var(--muted);
  padding: 0 12px;
  text-align: left;
}

.mode-button:hover {
  border-color: var(--line);
  color: var(--ink);
}

.mode-button.active {
  background: var(--surface-soft);
  color: var(--teal-dark);
  font-weight: 700;
}

.rail-note {
  margin-top: auto;
  border-top: 1px solid var(--line);
  padding-top: 18px;
}

.rail-note strong,
.rail-note span {
  display: block;
}

.rail-note strong {
  font-size: 14px;
}

.rail-note span {
  margin-top: 8px;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.6;
}

.quiz-panel {
  display: flex;
  flex-direction: column;
  gap: 18px;
  padding: 8px 0;
}

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

.section-label {
  margin: 0 0 8px;
  color: var(--teal);
  font-size: 14px;
  font-weight: 700;
}

.topbar h2 {
  margin: 0;
  font-size: 30px;
  line-height: 1.25;
}

.icon-button {
  display: grid;
  width: 42px;
  height: 42px;
  flex: 0 0 auto;
  place-items: center;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  font-size: 20px;
}

.icon-button:hover {
  border-color: var(--teal);
  color: var(--teal-dark);
}

.stats-strip {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 10px;
}

.stats-strip div {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  padding: 14px;
}

.stats-strip span {
  display: block;
  font-size: 23px;
  font-weight: 800;
  line-height: 1;
}

.stats-strip small {
  display: block;
  margin-top: 8px;
  color: var(--muted);
  font-size: 12px;
}

.chapter-picker {
  display: flex;
  gap: 8px;
  overflow-x: auto;
  padding-bottom: 2px;
}

.chapter-chip {
  min-width: max-content;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--muted);
  padding: 9px 12px;
}

.chapter-chip.active {
  border-color: var(--teal);
  background: var(--teal);
  color: #ffffff;
  font-weight: 700;
}

.question-surface {
  display: flex;
  min-height: 520px;
  flex: 1;
}

.question-card,
.paper-view,
.empty-state {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.question-card {
  display: flex;
  flex-direction: column;
  padding: 28px;
  touch-action: pan-y;
  will-change: opacity, transform;
}

.question-card.card-enter-next {
  animation: card-enter-next 180ms cubic-bezier(0.4, 0, 0.2, 1) both;
}

.question-card.card-enter-prev {
  animation: card-enter-prev 180ms cubic-bezier(0.4, 0, 0.2, 1) both;
}

.question-card.card-enter-soft {
  animation: card-enter-soft 200ms ease-out both;
}

.question-card.card-exit-next {
  animation: card-exit-next 130ms cubic-bezier(0.4, 0, 1, 1) both;
  pointer-events: none;
}

.question-card.card-exit-prev {
  animation: card-exit-prev 130ms cubic-bezier(0.4, 0, 1, 1) both;
  pointer-events: none;
}

.question-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 20px;
}

.meta-tag {
  border-radius: 8px;
  background: var(--surface-soft);
  color: var(--teal-dark);
  padding: 7px 10px;
  font-size: 13px;
  font-weight: 700;
}

.question-text {
  flex: 1;
  min-height: 190px;
  margin: 0;
  font-size: 26px;
  font-weight: 700;
  line-height: 1.62;
  overflow-wrap: anywhere;
}

.answer-row {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin-top: 24px;
}

.answer-button {
  min-height: 72px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  font-size: 20px;
  font-weight: 800;
  transition:
    border-color 150ms ease,
    background 150ms ease,
    color 150ms ease,
    transform 150ms ease;
}

.answer-button:hover {
  border-color: var(--teal);
}

.answer-button:active,
.primary-button:active,
.secondary-button:active,
.primary-link:active,
.ghost-link:active {
  transform: scale(0.985);
}

.answer-button:disabled {
  cursor: default;
}

.answer-button.correct-choice {
  border-color: rgba(31, 122, 74, 0.35);
  background: rgba(31, 122, 74, 0.1);
  color: var(--green);
}

.answer-button.wrong-choice {
  border-color: rgba(185, 65, 59, 0.35);
  background: rgba(185, 65, 59, 0.1);
  color: var(--red);
}

.feedback {
  display: none;
  margin-top: 18px;
  border-left: 4px solid var(--teal);
  border-radius: 8px;
  background: var(--surface-soft);
  padding: 16px;
  line-height: 1.7;
}

.feedback.show {
  display: block;
}

.feedback-rise {
  animation: feedback-rise 190ms ease-out both;
}

.feedback strong {
  display: block;
  margin-bottom: 4px;
}

.feedback.correct {
  border-color: var(--green);
}

.feedback.wrong {
  border-color: var(--red);
}

.card-actions {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 10px;
  margin-top: 20px;
}

.primary-button,
.secondary-button,
.primary-link,
.ghost-link {
  display: inline-flex;
  min-height: 42px;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  padding: 0 16px;
  text-decoration: none;
  font-weight: 700;
  transition:
    border-color 150ms ease,
    background 150ms ease,
    color 150ms ease,
    transform 150ms ease;
}

.primary-button,
.primary-link {
  border: 1px solid var(--teal);
  background: var(--teal);
  color: #ffffff;
}

.primary-button:hover,
.primary-link:hover {
  background: var(--teal-dark);
}

.secondary-button,
.ghost-link {
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--ink);
}

.secondary-button:hover,
.ghost-link:hover {
  border-color: var(--teal);
  color: var(--teal-dark);
}

.progress-dots {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 20px;
}

.swipe-hint {
  margin: 12px 0 0;
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
  text-align: center;
}

.dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--line);
}

.dot.active {
  background: var(--teal);
}

.dot.done {
  background: rgba(28, 124, 104, 0.42);
}

.study-panel {
  display: flex;
  flex-direction: column;
  gap: 16px;
  border-left: 1px solid var(--line);
  padding: 8px 0 8px 24px;
}

.side-section {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  padding: 18px;
}

.side-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 14px;
}

.side-heading span {
  color: var(--muted);
  font-size: 13px;
  font-weight: 700;
}

.side-heading strong {
  color: var(--ink);
  font-size: 14px;
}

.chapter-list {
  display: grid;
  gap: 10px;
}

.chapter-row {
  display: grid;
  gap: 6px;
}

.chapter-row button {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  border: 0;
  border-radius: 8px;
  background: var(--surface-soft);
  color: var(--ink);
  padding: 10px;
  text-align: left;
}

.chapter-row button:hover {
  color: var(--teal-dark);
}

.mini-bar {
  height: 6px;
  overflow: hidden;
  border-radius: 999px;
  background: var(--line);
}

.mini-bar span {
  display: block;
  height: 100%;
  border-radius: inherit;
  background: var(--teal);
}

.pdf-box p {
  margin: 0 0 14px;
  color: var(--muted);
  font-size: 14px;
  line-height: 1.7;
}

.pdf-actions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
}

.paper-view,
.empty-state {
  padding: 28px;
}

.paper-view h3,
.empty-state h3 {
  margin: 0 0 10px;
  font-size: 24px;
}

.paper-view p,
.empty-state p {
  margin: 0;
  color: var(--muted);
  line-height: 1.7;
}

.paper-list {
  display: grid;
  gap: 10px;
  margin-top: 18px;
}

.paper-item {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
}

.paper-item strong {
  display: block;
  margin-bottom: 6px;
  color: var(--teal-dark);
  font-size: 13px;
}

.paper-item span {
  display: block;
  color: var(--ink);
  line-height: 1.6;
}

.paper-item .paper-explanation {
  margin-top: 8px;
  padding-top: 8px;
  border-top: 1px dashed var(--line);
  color: var(--muted);
  font-size: 13px;
}

@keyframes card-enter-next {
  from {
    opacity: 0;
    transform: translateX(18px) translateY(4px) scale(0.985);
  }
  to {
    opacity: 1;
    transform: translateX(0) translateY(0) scale(1);
  }
}

@keyframes card-enter-prev {
  from {
    opacity: 0;
    transform: translateX(-18px) translateY(4px) scale(0.985);
  }
  to {
    opacity: 1;
    transform: translateX(0) translateY(0) scale(1);
  }
}

@keyframes card-enter-soft {
  from {
    opacity: 0;
    transform: translateY(8px) scale(0.99);
  }
  to {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

@keyframes card-exit-next {
  from {
    opacity: 1;
    transform: translateX(0) scale(1);
  }
  to {
    opacity: 0;
    transform: translateX(-16px) scale(0.985);
  }
}

@keyframes card-exit-prev {
  from {
    opacity: 1;
    transform: translateX(0) scale(1);
  }
  to {
    opacity: 0;
    transform: translateX(16px) scale(0.985);
  }
}

@keyframes feedback-rise {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (prefers-reduced-motion: reduce) {
  .question-card,
  .question-card.card-enter-next,
  .question-card.card-enter-prev,
  .question-card.card-enter-soft,
  .question-card.card-exit-next,
  .question-card.card-exit-prev,
  .feedback-rise {
    animation: none !important;
    transform: none !important;
  }

  .answer-button,
  .primary-button,
  .secondary-button,
  .primary-link,
  .ghost-link {
    transition: none !important;
  }
}

@media (max-width: 1120px) {
  .app-shell {
    grid-template-columns: 210px minmax(0, 1fr);
  }

  .study-panel {
    grid-column: 1 / -1;
    border-left: 0;
    border-top: 1px solid var(--line);
    padding: 20px 0 0;
  }
}

@media (max-width: 760px) {
  .app-shell {
    display: flex;
    flex-direction: column;
    gap: 12px;
    padding: 12px;
  }

  .rail {
    gap: 14px;
    border-right: 0;
    border-bottom: 1px solid var(--line);
    padding: 0 0 12px;
  }

  .brand {
    gap: 10px;
  }

  .brand-mark {
    width: 38px;
    height: 38px;
    font-size: 20px;
  }

  .brand h1 {
    font-size: 24px;
  }

  .brand p {
    margin-top: 2px;
    font-size: 12px;
  }

  .mode-nav {
    display: grid;
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 6px;
  }

  .mode-button {
    min-height: 38px;
    justify-content: center;
    padding: 0 6px;
    font-size: 13px;
    text-align: center;
  }

  .rail-note {
    display: none;
  }

  .quiz-panel {
    gap: 12px;
    padding: 0;
  }

  .topbar {
    align-items: center;
  }

  .section-label {
    margin-bottom: 4px;
    font-size: 13px;
  }

  .topbar h2 {
    font-size: 22px;
  }

  .icon-button {
    width: 40px;
    height: 40px;
  }

  .stats-strip {
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 6px;
  }

  .stats-strip div {
    min-height: 54px;
    padding: 8px 6px;
  }

  .stats-strip span {
    font-size: 20px;
  }

  .stats-strip small {
    margin-top: 4px;
    font-size: 11px;
    white-space: nowrap;
  }

  .chapter-picker {
    gap: 6px;
    margin: -2px -12px 0;
    padding: 0 12px 2px;
  }

  .chapter-chip {
    padding: 8px 10px;
  }

  .question-surface {
    min-height: auto;
  }

  .question-card,
  .paper-view,
  .empty-state {
    padding: 16px;
  }

  .question-meta {
    gap: 6px;
    margin-bottom: 14px;
  }

  .meta-tag {
    padding: 6px 8px;
    font-size: 12px;
  }

  .question-text {
    min-height: 128px;
    font-size: 20px;
    line-height: 1.5;
  }

  .answer-row {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 8px;
    margin-top: 18px;
  }

  .pdf-actions {
    grid-template-columns: 1fr;
  }

  .answer-button {
    min-height: 60px;
    font-size: 18px;
  }

  .feedback {
    margin-top: 14px;
    padding: 14px;
    line-height: 1.55;
  }

  .card-actions {
    gap: 8px;
    margin-top: 14px;
  }

  .primary-button,
  .secondary-button,
  .primary-link,
  .ghost-link {
    min-height: 44px;
    padding: 0 14px;
  }

  .progress-dots {
    max-height: 32px;
    gap: 5px;
    margin-top: 16px;
    overflow: hidden;
  }

  .swipe-hint {
    margin-top: 10px;
  }

  .study-panel {
    gap: 12px;
    padding-top: 14px;
  }
}

@media (max-width: 420px) {
  .brand h1 {
    font-size: 22px;
  }

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

  .mode-button {
    font-size: 12px;
  }

  .stats-strip span {
    font-size: 19px;
  }

  .question-text {
    font-size: 19px;
  }
}