:root {
  color-scheme: light;
  --ink: #20242a;
  --muted: #66707c;
  --line: #d8dee7;
  --panel: #ffffff;
  --surface: #f5f7fa;
  --blue: #1768ac;
  --blue-dark: #0d4f87;
  --teal: #0f766e;
  --green: #1f7a4d;
  --red: #b42318;
  --amber: #986f0b;
  --shadow: 0 20px 45px rgba(25, 37, 54, 0.12);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at top left, rgba(23, 104, 172, 0.12), transparent 30rem),
    linear-gradient(135deg, #f7f9fc 0%, #eef4f6 55%, #f7f8fb 100%);
  color: var(--ink);
  font-family: "Segoe UI", "Microsoft JhengHei", system-ui, sans-serif;
}

button {
  font: inherit;
}

.app-shell {
  width: min(1180px, calc(100% - 32px));
  min-height: 100vh;
  margin: 0 auto;
  padding: 32px 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr) 340px;
  gap: 24px;
  align-items: start;
}

.practice-panel,
.review-panel {
  background: rgba(255, 255, 255, 0.92);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}

.practice-panel {
  min-height: calc(100vh - 64px);
  padding: 28px;
  display: flex;
  flex-direction: column;
  gap: 22px;
}

.review-panel {
  padding: 22px;
  position: sticky;
  top: 24px;
}

.topbar {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  align-items: start;
}

.eyebrow {
  margin: 0 0 8px;
  color: var(--teal);
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0;
  text-transform: uppercase;
}

h1,
h2,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 0;
  font-size: clamp(2rem, 4vw, 3.4rem);
  line-height: 1.05;
  letter-spacing: 0;
}

.status-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  border: 1px solid var(--line);
  background: var(--surface);
}

.status-grid div {
  padding: 16px;
  border-right: 1px solid var(--line);
}

.status-grid div:last-child {
  border-right: 0;
}

.status-grid span {
  display: block;
  margin-bottom: 6px;
  color: var(--muted);
  font-size: 0.86rem;
}

.status-grid strong {
  display: block;
  min-height: 1.4em;
  font-size: 1rem;
}

.question-area {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  min-height: 280px;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  padding: 28px 0;
}

.question-number {
  color: var(--blue);
  font-weight: 800;
}

#questionText {
  max-width: 920px;
  margin-bottom: 16px;
  font-size: clamp(1.45rem, 3vw, 2.4rem);
  line-height: 1.28;
  letter-spacing: 0;
}

.hint {
  max-width: 760px;
  margin-bottom: 0;
  color: var(--muted);
  line-height: 1.7;
}

.answer-label {
  display: block;
  margin-bottom: 10px;
  color: var(--muted);
  font-weight: 700;
}

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

.concept-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.concept-btn {
  width: 100%;
  min-height: 86px;
  border: 1px solid var(--line);
  padding: 14px;
  background: #fff;
  color: var(--ink);
  text-align: left;
  display: grid;
  gap: 4px;
}

.concept-btn:hover,
.concept-btn.active {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px rgba(23, 104, 172, 0.14);
}

.concept-btn strong {
  color: var(--blue-dark);
  font-size: 1rem;
}

.concept-btn span {
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.45;
}

.options-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.option-btn {
  width: 100%;
  min-height: 64px;
  border: 1px solid var(--line);
  padding: 14px 16px;
  color: var(--ink);
  background: #fff;
  text-align: left;
  outline: none;
  display: flex;
  gap: 12px;
  align-items: center;
  line-height: 1.45;
}

.option-btn::before {
  content: attr(data-letter);
  flex: 0 0 30px;
  width: 30px;
  height: 30px;
  border: 1px solid var(--line);
  display: grid;
  place-items: center;
  color: var(--blue-dark);
  background: var(--surface);
  font-weight: 800;
}

.option-btn:hover:not(:disabled),
.option-btn.selected {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px rgba(23, 104, 172, 0.14);
}

.option-btn.selected::before {
  border-color: var(--blue);
  background: var(--blue);
  color: #fff;
}

.option-btn.correct-choice {
  border-color: rgba(31, 122, 77, 0.55);
  background: #edf7f1;
}

.option-btn.wrong-choice {
  border-color: rgba(180, 35, 24, 0.55);
  background: #fff0ef;
}

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

button {
  min-height: 44px;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  padding: 0 16px;
  cursor: pointer;
  font-weight: 700;
}

button:hover:not(:disabled) {
  border-color: var(--blue);
  color: var(--blue-dark);
}

button:disabled {
  cursor: not-allowed;
  color: #98a2b3;
  background: #f1f3f5;
}

button.primary {
  border-color: var(--blue);
  background: var(--blue);
  color: #fff;
}

button.primary:hover:not(:disabled) {
  background: var(--blue-dark);
  color: #fff;
}

.voice-picker {
  min-height: 44px;
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--muted);
  font-weight: 700;
}

.voice-picker select {
  min-height: 44px;
  max-width: min(420px, 100%);
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  padding: 0 12px;
  font: inherit;
  font-weight: 600;
}

.voice-picker select:focus {
  border-color: var(--blue);
  outline: none;
  box-shadow: 0 0 0 3px rgba(23, 104, 172, 0.14);
}

.feedback {
  min-height: 58px;
  border: 1px solid var(--line);
  padding: 14px 16px;
  line-height: 1.6;
  background: var(--surface);
}

.feedback.correct {
  border-color: rgba(31, 122, 77, 0.35);
  color: var(--green);
  background: #edf7f1;
}

.feedback.wrong {
  border-color: rgba(180, 35, 24, 0.35);
  color: var(--red);
  background: #fff0ef;
}

.feedback.neutral {
  color: var(--muted);
}

.feedback.listening {
  border-color: rgba(152, 111, 11, 0.35);
  color: var(--amber);
  background: #fff8e5;
}

.review-panel h2 {
  margin-bottom: 16px;
  font-size: 1.3rem;
}

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

.topic-item {
  border: 1px solid var(--line);
  padding: 12px;
  background: var(--surface);
}

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

.topic-item span {
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.45;
}

@media (max-width: 900px) {
  .app-shell {
    grid-template-columns: 1fr;
  }

  .practice-panel {
    min-height: auto;
  }

  .review-panel {
    position: static;
  }
}

@media (max-width: 620px) {
  .app-shell {
    width: min(100% - 20px, 1180px);
    padding: 10px 0;
  }

  .practice-panel,
  .review-panel {
    padding: 18px;
  }

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

  .score-card {
    text-align: left;
  }

  .status-grid div {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .status-grid div:last-child {
    border-bottom: 0;
  }

  button {
    flex: 1 1 145px;
  }

  .options-list,
  .concept-list {
    grid-template-columns: 1fr;
  }
}