:root {
  color-scheme: light dark;
  --bg: #f5f6f4;
  --bg-grad: radial-gradient(1200px 600px at 100% -10%, #eef1ee 0%, transparent 60%);
  --panel: #ffffff;
  --panel-strong: #f0f3f1;
  --text: #1f2528;
  --muted: #667076;
  --line: #d8dedb;
  --line-soft: #e6eae7;
  --accent: #b33b32;
  --accent-dark: #8f2d27;
  --accent-soft: rgba(179, 59, 50, 0.12);
  --teal: #267764;
  --amber: #a86f18;
  --blue: #315f8f;
  --blue-soft: rgba(49, 95, 143, 0.14);
  --wrong: #c83a32;
  --right: #28734f;
  --shadow: 0 18px 50px rgba(31, 37, 40, 0.08);
  --shadow-sm: 0 2px 8px rgba(31, 37, 40, 0.06);
  --radius: 10px;
  --radius-sm: 7px;
  --ease: cubic-bezier(0.22, 0.61, 0.36, 1);
  font-family: "Microsoft YaHei", "PingFang SC", "Segoe UI", Arial, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14181a;
    --bg-grad: radial-gradient(1200px 600px at 100% -10%, #1d2427 0%, transparent 60%);
    --panel: #1b2124;
    --panel-strong: #232b2f;
    --text: #e8ecea;
    --muted: #94a1a4;
    --line: #2f383c;
    --line-soft: #29312f;
    --accent: #d9564c;
    --accent-dark: #c3453c;
    --accent-soft: rgba(217, 86, 76, 0.18);
    --teal: #3fa285;
    --amber: #d0a24a;
    --blue: #6ea3d8;
    --blue-soft: rgba(110, 163, 216, 0.18);
    --wrong: #e46a61;
    --right: #4fb488;
    --shadow: 0 18px 50px rgba(0, 0, 0, 0.45);
    --shadow-sm: 0 2px 10px rgba(0, 0, 0, 0.35);
  }
}

* {
  box-sizing: border-box;
}

html,
body {
  min-height: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  background-image: var(--bg-grad);
  background-attachment: fixed;
  color: var(--text);
  letter-spacing: 0;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

button,
input,
select,
textarea {
  font: inherit;
  letter-spacing: 0;
}

button {
  border: 0;
  cursor: pointer;
}

button:disabled,
input:disabled,
select:disabled {
  cursor: not-allowed;
  opacity: 0.5;
}

:focus-visible {
  outline: 2px solid var(--blue);
  outline-offset: 2px;
}

.app-shell {
  display: grid;
  grid-template-columns: 344px minmax(0, 1fr);
  gap: 20px;
  min-height: 100vh;
  padding: 18px;
}

.sidebar {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  gap: 18px;
  padding: 18px;
  position: sticky;
  top: 18px;
  height: calc(100vh - 36px);
  min-width: 0;
  overflow: auto;
  scrollbar-width: thin;
  scrollbar-color: var(--line) transparent;
}

.sidebar::-webkit-scrollbar {
  width: 8px;
}

.sidebar::-webkit-scrollbar-thumb {
  background: var(--line);
  border-radius: 99px;
}

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

.brand-mark {
  align-items: center;
  background: linear-gradient(135deg, var(--accent), var(--accent-dark));
  border-radius: var(--radius-sm);
  color: #ffffff;
  display: flex;
  flex: 0 0 44px;
  font-size: 24px;
  font-weight: 800;
  height: 44px;
  justify-content: center;
  box-shadow: 0 4px 12px var(--accent-soft);
}

.brand h1,
.workspace-head h2,
.empty-state h2 {
  margin: 0;
}

.brand h1 {
  font-size: 24px;
  line-height: 1.15;
}

.brand p,
.workspace-head p {
  color: var(--muted);
  margin: 5px 0 0;
}

.countdown {
  align-items: center;
  background: var(--panel-strong);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  display: flex;
  justify-content: space-between;
  min-height: 48px;
  padding: 10px 12px;
  min-width: 0;
}

.countdown span {
  color: var(--muted);
}

.countdown strong {
  color: var(--accent-dark);
  font-size: 20px;
  min-width: 0;
  white-space: nowrap;
  font-variant-numeric: tabular-nums;
}

.stats {
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  min-width: 0;
  overflow: hidden;
}

.stats div {
  border-bottom: 1px solid var(--line-soft);
  min-height: 74px;
  padding: 12px 6px;
  transition: background 160ms var(--ease);
}

.stats div:hover {
  background: var(--panel-strong);
}

.stats div:nth-child(odd) {
  border-right: 1px solid var(--line-soft);
}

.stats div:nth-last-child(-n + 2) {
  border-bottom: 0;
}

.stats strong,
.stats span {
  display: block;
  text-align: center;
}

.stats strong {
  font-size: 26px;
  line-height: 1.2;
  font-variant-numeric: tabular-nums;
}

.stats span {
  color: var(--muted);
  margin-top: 4px;
}

.controls {
  display: grid;
  gap: 8px;
  min-width: 0;
}

.controls label,
.control-label {
  color: var(--muted);
  font-size: 14px;
  font-weight: 700;
}

.controls select,
.controls input,
.subjective-box textarea {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  color: var(--text);
  min-height: 42px;
  min-width: 0;
  outline: none;
  padding: 9px 10px;
  width: 100%;
  transition: border-color 140ms var(--ease), box-shadow 140ms var(--ease);
}

.controls select:hover,
.controls input:hover {
  border-color: var(--muted);
}

.controls select:focus,
.controls input:focus,
.subjective-box textarea:focus {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px var(--blue-soft);
}

.segmented {
  background: var(--panel-strong);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  min-width: 0;
  padding: 3px;
}

.segmented button {
  background: transparent;
  border-radius: 6px;
  color: var(--muted);
  min-height: 36px;
  transition: color 140ms var(--ease), background 140ms var(--ease), box-shadow 140ms var(--ease);
}

.segmented button.is-active {
  background: var(--panel);
  color: var(--text);
  font-weight: 800;
  box-shadow: var(--shadow-sm);
}

.toggle-row {
  align-items: center;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  min-height: 44px;
  padding: 9px 10px;
  transition: border-color 140ms var(--ease);
}

.toggle-row:hover {
  border-color: var(--muted);
}

.toggle-row span {
  color: var(--text);
  font-weight: 800;
}

.toggle-row input {
  appearance: none;
  background: var(--line);
  border: 0;
  border-radius: 999px;
  flex: 0 0 auto;
  height: 24px;
  min-height: 24px;
  padding: 0;
  position: relative;
  transition: background 160ms var(--ease);
  width: 44px;
}

.toggle-row input::after {
  background: #ffffff;
  border-radius: 50%;
  box-shadow: 0 1px 4px rgba(31, 37, 40, 0.22);
  content: "";
  height: 20px;
  left: 2px;
  position: absolute;
  top: 2px;
  transition: transform 160ms var(--ease);
  width: 20px;
}

.toggle-row input:checked {
  background: var(--accent);
}

.toggle-row input:checked::after {
  transform: translateX(20px);
}

.toggle-row input:focus-visible {
  box-shadow: 0 0 0 3px var(--accent-soft);
}

.button-stack {
  display: grid;
  gap: 8px;
  margin-top: 4px;
}

.memory-actions {
  display: grid;
  gap: 8px;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.memory-status {
  background: var(--panel-strong);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  color: var(--muted);
  font-size: 13px;
  font-weight: 800;
  min-height: 34px;
  padding: 8px 10px;
  text-align: center;
}

.primary-btn,
.secondary-btn,
.plain-btn,
.icon-btn {
  align-items: center;
  border-radius: var(--radius-sm);
  display: inline-flex;
  justify-content: center;
  min-height: 42px;
  padding: 9px 14px;
  transition: background 140ms var(--ease), border-color 140ms var(--ease),
    transform 80ms var(--ease), box-shadow 140ms var(--ease);
}

.primary-btn:active,
.secondary-btn:active,
.plain-btn:active,
.icon-btn:active,
.option-btn:active,
.nav-dot:active {
  transform: translateY(1px);
}

.primary-btn {
  background: var(--accent);
  color: #ffffff;
  font-weight: 800;
  box-shadow: 0 4px 14px var(--accent-soft);
}

.primary-btn:hover {
  background: var(--accent-dark);
  box-shadow: 0 6px 18px var(--accent-soft);
}

.secondary-btn {
  background: color-mix(in srgb, var(--teal) 12%, var(--panel));
  color: var(--teal);
  font-weight: 800;
}

.secondary-btn:hover {
  background: color-mix(in srgb, var(--teal) 20%, var(--panel));
}

.plain-btn {
  background: var(--panel);
  border: 1px solid var(--line);
  color: var(--text);
}

.plain-btn:hover {
  background: var(--panel-strong);
  border-color: var(--muted);
}

.icon-btn {
  background: var(--panel);
  border: 1px solid var(--line);
  color: var(--amber);
  font-size: 23px;
  height: 42px;
  line-height: 1;
  padding: 0;
  width: 42px;
}

.icon-btn:hover {
  border-color: var(--amber);
}

.icon-btn.is-active {
  background: color-mix(in srgb, var(--amber) 16%, var(--panel));
  border-color: var(--amber);
  animation: pop 240ms var(--ease);
}

@keyframes pop {
  0% { transform: scale(1); }
  45% { transform: scale(1.22); }
  100% { transform: scale(1); }
}

.workspace {
  display: grid;
  gap: 14px;
  grid-template-rows: auto auto auto auto minmax(110px, auto);
  min-width: 0;
  width: 100%;
  max-width: 1040px;
  margin-inline: auto;
}

.workspace-head {
  align-items: center;
  display: flex;
  gap: 16px;
  justify-content: space-between;
  min-height: 76px;
}

.workspace-head h2 {
  font-size: 24px;
  line-height: 1.25;
}

.mode-label {
  color: var(--accent-dark);
  font-size: 13px;
  font-weight: 800;
  letter-spacing: 0.04em;
  margin-bottom: 4px;
  text-transform: uppercase;
}

.head-actions {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: flex-end;
}

.notice {
  background: color-mix(in srgb, var(--amber) 14%, var(--panel));
  border: 1px solid color-mix(in srgb, var(--amber) 45%, var(--panel));
  border-radius: var(--radius-sm);
  color: var(--amber);
  padding: 11px 12px;
  animation: slide-in 220ms var(--ease);
}

.notice.is-good {
  background: color-mix(in srgb, var(--right) 12%, var(--panel));
  border-color: color-mix(in srgb, var(--right) 40%, var(--panel));
  color: var(--right);
}

.notice.is-bad {
  background: color-mix(in srgb, var(--wrong) 12%, var(--panel));
  border-color: color-mix(in srgb, var(--wrong) 40%, var(--panel));
  color: var(--wrong);
}

@keyframes slide-in {
  from { opacity: 0; transform: translateY(-6px); }
  to { opacity: 1; transform: translateY(0); }
}

.progress-track {
  background: var(--line);
  border-radius: 99px;
  height: 9px;
  overflow: hidden;
}

#progressBar {
  background: linear-gradient(90deg, var(--accent), var(--accent-dark));
  height: 100%;
  transition: width 320ms var(--ease);
  width: 0;
}

.quiz-card,
.empty-state {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 30px 34px;
}

.quiz-card {
  animation: card-in 260ms var(--ease);
}

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

.question-body {
  display: grid;
  gap: 22px;
  grid-template-columns: minmax(0, 1fr);
}

.prompt-pane,
.choice-pane {
  min-width: 0;
}

.prompt-pane {
  border-bottom: 1px solid var(--line-soft);
  padding-bottom: 20px;
}

.question-meta {
  align-items: center;
  display: flex;
  gap: 12px;
  justify-content: space-between;
  margin-bottom: 16px;
}

.badges {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.badge {
  align-items: center;
  background: var(--panel-strong);
  border: 1px solid var(--line);
  border-radius: 99px;
  color: var(--muted);
  display: inline-flex;
  font-size: 13px;
  font-weight: 700;
  min-height: 26px;
  padding: 3px 9px;
}

.badge.type {
  background: color-mix(in srgb, var(--blue) 12%, var(--panel));
  border-color: color-mix(in srgb, var(--blue) 35%, var(--panel));
  color: var(--blue);
}

.badge.diff {
  background: color-mix(in srgb, var(--amber) 14%, var(--panel));
  border-color: color-mix(in srgb, var(--amber) 38%, var(--panel));
  color: var(--amber);
}

.badge.memory {
  background: color-mix(in srgb, var(--right) 12%, var(--panel));
  border-color: color-mix(in srgb, var(--right) 38%, var(--panel));
  color: var(--right);
}

#questionCounter {
  color: var(--muted);
  flex: 0 0 auto;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.question-text {
  font-size: 24px;
  line-height: 1.7;
  margin: 0;
  white-space: pre-wrap;
  letter-spacing: 0.005em;
}

.options-list {
  display: grid;
  gap: 13px;
}

.option-btn {
  align-items: flex-start;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  color: var(--text);
  display: grid;
  gap: 13px;
  grid-template-columns: 36px minmax(0, 1fr);
  min-height: 58px;
  padding: 13px 15px;
  text-align: left;
  width: 100%;
  font-size: 16.5px;
  transition: border-color 140ms var(--ease), background 140ms var(--ease),
    box-shadow 140ms var(--ease), transform 80ms var(--ease);
}

.option-btn:hover {
  border-color: var(--muted);
  background: var(--panel-strong);
}

.option-btn.is-selected {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px var(--blue-soft);
}

.option-btn.is-keyboard {
  border-color: var(--blue);
  box-shadow: inset 0 0 0 1px var(--blue);
}

.option-btn.is-correct {
  background: color-mix(in srgb, var(--right) 12%, var(--panel));
  border-color: var(--right);
}

.option-btn.is-wrong {
  background: color-mix(in srgb, var(--wrong) 12%, var(--panel));
  border-color: var(--wrong);
}

.option-letter {
  align-items: center;
  background: var(--panel-strong);
  border: 1px solid var(--line);
  border-radius: 7px;
  color: var(--muted);
  display: inline-flex;
  font-weight: 800;
  height: 36px;
  justify-content: center;
  width: 36px;
  transition: background 140ms var(--ease), color 140ms var(--ease), border-color 140ms var(--ease);
}

.option-btn.is-selected .option-letter,
.option-btn.is-correct .option-letter {
  background: var(--teal);
  border-color: var(--teal);
  color: #ffffff;
}

.option-btn.is-wrong .option-letter {
  background: var(--wrong);
  border-color: var(--wrong);
  color: #ffffff;
}

.option-text {
  line-height: 1.65;
  min-width: 0;
  overflow-wrap: anywhere;
  align-self: center;
}

.subjective-box {
  display: grid;
  gap: 12px;
}

.subjective-box textarea {
  line-height: 1.65;
  min-height: 170px;
  resize: vertical;
}

.subjective-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.answer-panel {
  background: var(--panel-strong);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  margin-top: 16px;
  padding: 14px;
  animation: slide-in 220ms var(--ease);
}

.answer-line {
  align-items: baseline;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-bottom: 8px;
}

.answer-line span {
  color: var(--muted);
  font-weight: 700;
}

.answer-line strong {
  color: var(--right);
  font-size: 19px;
}

.answer-panel p {
  line-height: 1.7;
  margin: 8px 0 0;
  white-space: pre-wrap;
}

#explanationText {
  color: var(--muted);
}

.actions {
  display: grid;
  gap: 10px;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  margin-top: 14px;
}

.empty-state {
  text-align: center;
}

.empty-state p {
  color: var(--muted);
}

.question-strip {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 10px;
}

.nav-head {
  align-items: center;
  display: flex;
  gap: 10px;
  justify-content: space-between;
  margin-bottom: 8px;
}

.nav-head span {
  color: var(--muted);
  font-size: 13px;
  font-weight: 800;
}

.nav-head .plain-btn {
  font-size: 13px;
  min-height: 32px;
  padding: 5px 10px;
}

#navGrid {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  min-height: 34px;
}

.nav-dot {
  align-items: center;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 6px;
  color: var(--muted);
  display: inline-flex;
  font-size: 13px;
  font-weight: 700;
  height: 32px;
  justify-content: center;
  min-width: 34px;
  padding: 0 6px;
  font-variant-numeric: tabular-nums;
  transition: border-color 120ms var(--ease), background 120ms var(--ease),
    transform 80ms var(--ease);
}

.nav-dot:hover {
  border-color: var(--muted);
}

.nav-dot.is-current {
  border-color: var(--accent);
  color: var(--accent-dark);
  box-shadow: inset 0 0 0 1px var(--accent);
}

.nav-dot.is-done {
  background: color-mix(in srgb, var(--right) 12%, var(--panel));
  border-color: color-mix(in srgb, var(--right) 38%, var(--panel));
  color: var(--right);
}

.nav-dot.is-memory {
  background: color-mix(in srgb, var(--right) 8%, var(--panel));
  border-color: color-mix(in srgb, var(--right) 32%, var(--panel));
  color: var(--right);
}

.nav-dot.is-wrong {
  background: color-mix(in srgb, var(--wrong) 12%, var(--panel));
  border-color: color-mix(in srgb, var(--wrong) 38%, var(--panel));
  color: var(--wrong);
}

.nav-dot.is-favorite::after {
  color: var(--amber);
  content: "★";
  font-size: 10px;
  margin-left: 2px;
}

.nav-ellipsis {
  align-items: center;
  color: var(--muted);
  display: inline-flex;
  height: 32px;
  justify-content: center;
  min-width: 22px;
}

[hidden] {
  display: none !important;
}

@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

@media (max-width: 960px) {
  .app-shell {
    grid-template-columns: 1fr;
    padding: 12px;
  }

  .sidebar {
    height: auto;
    position: static;
  }

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

  .head-actions {
    justify-content: flex-start;
  }
}

@media (max-width: 620px) {
  .app-shell {
    gap: 12px;
    padding: 10px;
  }

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

  .actions {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .stats strong {
    font-size: 22px;
  }
}