:root {
  --bg: #f3f6fb;
  --surface: #ffffff;
  --surface-soft: #eaf0f8;
  --text: #162033;
  --muted: #5f6f89;
  --primary: #1f7aec;
  --primary-strong: #0f5fc3;
  --accent: #12a067;
  --danger: #d64d4d;
  --border: #d7e1ef;
  --shadow: 0 18px 48px rgba(25, 54, 95, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Microsoft YaHei", "PingFang SC", system-ui, sans-serif;
  background: linear-gradient(180deg, #f8fbff 0%, var(--bg) 100%);
  color: var(--text);
}

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

button {
  font: inherit;
}

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

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: blur(10px);
  background: rgba(248, 251, 255, 0.88);
  border-bottom: 1px solid rgba(215, 225, 239, 0.8);
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 72px;
  gap: 16px;
}

.brand {
  font-size: 20px;
  font-weight: 700;
}

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

.nav-links a {
  padding: 10px 14px;
  border-radius: 8px;
  color: var(--muted);
}

.nav-links a.is-active,
.nav-links a:hover {
  background: var(--surface-soft);
  color: var(--text);
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.6fr) minmax(280px, 0.9fr);
  gap: 24px;
  align-items: stretch;
  padding: 48px 0 28px;
}

.hero-copy,
.hero-panel,
.feature-block,
.toolbar,
.question-card,
.side-panel,
.mistakes-header,
.mistake-item,
.placeholder-block {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.hero-copy {
  padding: 40px;
  color: #ffffff;
  min-height: 360px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
}

.hero-copy-gradient {
  background:
    radial-gradient(circle at top left, rgba(94, 173, 255, 0.42), transparent 42%),
    radial-gradient(circle at 85% 20%, rgba(57, 210, 160, 0.28), transparent 32%),
    linear-gradient(135deg, #0f172a 0%, #164e63 45%, #1d4ed8 100%);
}

.eyebrow {
  margin: 0 0 8px;
  font-size: 14px;
  color: inherit;
  opacity: 0.82;
}

.hero-copy h1,
.placeholder-block h1,
.mistakes-header h1 {
  margin: 0;
  font-size: clamp(32px, 4vw, 46px);
  line-height: 1.1;
}

.lead,
.placeholder-block p,
.mistakes-header p {
  margin: 16px 0 0;
  font-size: 16px;
  line-height: 1.7;
}

.hero-actions,
.action-stack {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.hero-actions {
  margin-top: 24px;
}

.btn {
  min-height: 44px;
  padding: 0 18px;
  border-radius: 8px;
  border: 1px solid transparent;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: 0.18s ease;
}

.btn:disabled {
  cursor: not-allowed;
  opacity: 0.55;
}

.btn-primary {
  background: var(--primary);
  color: #ffffff;
}

.btn-primary:hover:not(:disabled) {
  background: var(--primary-strong);
}

.btn-secondary {
  background: var(--surface);
  border-color: var(--border);
  color: var(--text);
}

.btn-secondary:hover:not(:disabled) {
  background: var(--surface-soft);
}

.hero-panel {
  padding: 28px;
  display: grid;
  gap: 16px;
  align-content: center;
}

.metric {
  padding: 18px;
  border-radius: 8px;
  background: var(--surface-soft);
}

.metric-label,
.toolbar-label,
.question-number,
.progress-copy,
.feedback-meta,
.mistake-meta,
.empty-copy,
.empty-subcopy {
  color: var(--muted);
}

.metric strong {
  display: block;
  margin-top: 6px;
  font-size: 32px;
}

.section-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 20px;
  padding-bottom: 36px;
}

.feature-block {
  padding: 24px;
}

.feature-block h2 {
  margin: 0 0 10px;
  font-size: 22px;
}

.feature-block p {
  margin: 0;
  line-height: 1.7;
  color: var(--muted);
}

.practice-layout,
.mistakes-layout,
.placeholder-layout,
.exam-layout {
  padding: 28px 0 36px;
}

.toolbar {
  padding: 18px 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 20px;
}

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

.stats-inline {
  color: var(--muted);
}

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

.segmented {
  min-height: 40px;
  padding: 0 14px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--surface);
  cursor: pointer;
}

.segmented.is-active {
  background: var(--text);
  color: #ffffff;
  border-color: var(--text);
}

.question-stage {
  display: grid;
  grid-template-columns: minmax(0, 2fr) minmax(260px, 0.8fr);
  gap: 20px;
}

.question-card,
.side-panel,
.placeholder-block {
  padding: 24px;
}

.question-meta,
.mistake-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.tag {
  display: inline-flex;
  align-items: center;
  min-height: 32px;
  padding: 0 12px;
  border-radius: 999px;
  background: #e8f5ee;
  color: var(--accent);
  font-size: 14px;
  font-weight: 600;
}

.question-text {
  margin: 18px 0 20px;
  font-size: 28px;
  line-height: 1.45;
}

.options {
  display: grid;
  gap: 12px;
}

.option-btn {
  width: 100%;
  padding: 14px 16px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface);
  text-align: left;
  line-height: 1.6;
  cursor: pointer;
  transition: 0.18s ease;
}

.option-btn:hover:not(:disabled) {
  border-color: var(--primary);
  background: #f6faff;
}

.option-btn.is-correct {
  border-color: #8ed2b4;
  background: #edf9f2;
}

.option-btn.is-wrong {
  border-color: #ecb0b0;
  background: #fff1f1;
}

.feedback {
  margin-top: 18px;
  padding: 16px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #f9fbfe;
}

.feedback strong {
  font-size: 18px;
}

.feedback.is-correct strong {
  color: var(--accent);
}

.feedback.is-wrong strong {
  color: var(--danger);
}

.hidden {
  display: none;
}

.progress-card {
  padding-bottom: 18px;
}

.progress-bar {
  height: 12px;
  border-radius: 999px;
  background: var(--surface-soft);
  overflow: hidden;
}

.progress-value {
  height: 100%;
  width: 0%;
  background: linear-gradient(90deg, var(--primary) 0%, #35a6ff 100%);
}

.progress-copy {
  margin: 14px 0 0;
  line-height: 1.7;
}

.action-stack {
  margin-top: 18px;
}

.action-stack .btn {
  width: 100%;
}

.practice-mobile-nav {
  display: none;
}

.mistakes-header {
  padding: 22px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.mistakes-header h1 {
  font-size: 34px;
}

.mistakes-list {
  display: grid;
  gap: 16px;
  margin-top: 20px;
}

.exam-intro,
.exam-toolbar,
.paper-card,
.exam-question-card,
.exam-review-item {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.exam-intro {
  padding: 22px 24px;
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 20px;
}

.exam-intro h1 {
  margin: 0;
  font-size: 34px;
}

.exam-summary {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  color: var(--muted);
}

.exam-summary strong {
  color: var(--text);
}

.paper-grid {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 16px;
  margin-top: 20px;
}

.paper-card {
  padding: 20px;
  text-align: left;
  cursor: pointer;
  transition: 0.18s ease;
}

.paper-card:hover {
  border-color: var(--primary);
  transform: translateY(-2px);
}

.paper-kicker {
  display: block;
  color: var(--muted);
  font-size: 13px;
  margin-bottom: 8px;
}

.paper-card strong,
.result-score strong {
  display: block;
  font-size: 28px;
  line-height: 1.15;
}

.paper-meta {
  display: block;
  margin-top: 8px;
  color: var(--muted);
}

.exam-workspace {
  margin-top: 20px;
}

.exam-toolbar {
  padding: 18px 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.exam-toolbar-main,
.exam-toolbar-actions {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.exam-stage {
  display: grid;
  grid-template-columns: minmax(0, 2fr) minmax(320px, 0.95fr);
  gap: 20px;
  margin-top: 20px;
  align-items: start;
}

.exam-questions {
  display: grid;
  gap: 16px;
}

.exam-bottom-actions {
  margin-top: 20px;
  display: flex;
  justify-content: center;
  gap: 12px;
  flex-wrap: wrap;
}

.exam-bottom-actions .btn {
  min-width: 160px;
}

.exam-question-card,
.exam-review-item {
  padding: 20px;
}

.exam-mobile-paper-indicator {
  display: none;
}

.exam-option-list {
  display: grid;
  gap: 10px;
  margin-top: 16px;
}

.exam-option {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  line-height: 1.6;
}

.exam-option input {
  margin-top: 4px;
}

.exam-option.is-selected {
  border-color: var(--primary);
  background: #f6faff;
}

.exam-side {
  display: grid;
  gap: 16px;
  position: sticky;
  top: 92px;
}

.result-score {
  margin-bottom: 12px;
}

.result-metrics {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  color: var(--muted);
}

.exam-review-list {
  display: grid;
  gap: 14px;
  margin-top: 20px;
}

.exam-inline-feedback {
  margin-top: 14px;
  display: grid;
  gap: 6px;
  color: var(--muted);
}

.exam-inline-feedback.is-correct {
  color: var(--accent);
}

.exam-inline-feedback.is-wrong {
  color: var(--danger);
}

.review-correct {
  border-color: #8ed2b4;
}

.review-wrong {
  border-color: #ecb0b0;
}

.mistake-item {
  padding: 20px;
}

.mistake-title {
  margin: 0;
  font-size: 20px;
  line-height: 1.6;
}

.mistake-options {
  display: grid;
  gap: 8px;
  margin: 16px 0;
  color: var(--muted);
}

.mistake-answer-row {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  margin-top: 12px;
}

.answer-chip {
  display: inline-flex;
  align-items: center;
  min-height: 34px;
  padding: 0 12px;
  border-radius: 999px;
  background: var(--surface-soft);
}

.answer-chip.correct {
  background: #edf9f2;
  color: var(--accent);
}

.answer-chip.wrong {
  background: #fff1f1;
  color: var(--danger);
}

.mistake-actions {
  margin-top: 18px;
}

.empty-state {
  padding: 48px 24px;
  text-align: center;
  background: var(--surface);
  border: 1px dashed var(--border);
  border-radius: 8px;
}

.empty-copy {
  display: block;
  font-size: 22px;
}

.empty-subcopy {
  margin: 12px 0 0;
  line-height: 1.7;
}

.placeholder-layout {
  min-height: calc(100vh - 120px);
  display: grid;
  align-items: center;
}

.placeholder-block {
  max-width: 720px;
}

@media (max-width: 900px) {
  .hero,
  .section-grid,
  .question-stage,
  .exam-stage {
    grid-template-columns: 1fr;
  }

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

  .toolbar,
  .mistakes-header,
  .exam-intro,
  .exam-toolbar {
    align-items: flex-start;
    flex-direction: column;
  }

  .exam-side {
    position: static;
    top: auto;
  }
}

@media (max-width: 640px) {
  .shell {
    width: min(100% - 24px, 1120px);
  }

  .nav {
    min-height: auto;
    padding: 10px 0;
  }

  .brand {
    display: none;
  }

  .nav-links {
    width: 100%;
    flex-wrap: nowrap;
    gap: 6px;
  }

  .nav-links a {
    flex: 1 1 0;
    text-align: center;
    padding: 8px 6px;
    font-size: 13px;
    white-space: nowrap;
  }

  .nav-links a.is-active {
    background: var(--primary);
    color: #ffffff;
    font-weight: 700;
    box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.12);
  }

  .hero-copy,
  .hero-panel,
  .feature-block,
  .toolbar,
  .question-card,
  .side-panel,
  .mistakes-header,
  .mistake-item,
  .placeholder-block,
  .exam-intro,
  .exam-toolbar,
  .paper-card,
  .exam-question-card,
  .exam-review-item {
    padding-left: 18px;
    padding-right: 18px;
  }

  .hero-copy h1,
  .placeholder-block h1,
  .mistakes-header h1 {
    font-size: 24px;
  }

  .question-text {
    font-size: 16px;
  }

  .option-btn,
  .exam-option {
    padding: 10px 12px;
    min-height: 40px;
    font-size: 14px;
    line-height: 1.45;
  }

  .stats-inline {
    display: flex;
    flex-wrap: nowrap;
    gap: 12px;
    font-size: 14px;
  }

  .paper-grid {
    grid-template-columns: repeat(5, minmax(0, 1fr));
    gap: 6px;
  }

  .exam-toolbar {
    display: none;
  }

  .exam-mobile-paper-indicator {
    display: block;
    margin-bottom: 12px;
    padding: 10px 12px;
    border-radius: 8px;
    background: var(--primary);
    color: #ffffff;
    font-size: 14px;
    font-weight: 700;
    text-align: center;
  }

  .paper-card {
    padding: 10px 4px;
    text-align: center;
  }

  .result-score strong {
    font-size: 22px;
  }

  .paper-card strong {
    font-size: 14px;
    line-height: 1.2;
  }

  .paper-kicker {
    display: none;
  }

  .paper-meta {
    display: none;
  }

  .practice-layout {
    padding-bottom: 96px;
  }

  .side-panel .action-stack {
    display: none;
  }

  .practice-mobile-nav {
    position: fixed;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 20;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 8px;
    padding: 8px 12px calc(8px + env(safe-area-inset-bottom, 0px));
    border-top: 1px solid rgba(215, 225, 239, 0.92);
    background: rgba(248, 251, 255, 0.96);
    backdrop-filter: blur(10px);
    box-shadow: 0 -8px 24px rgba(25, 54, 95, 0.12);
  }

  .practice-mobile-nav .btn {
    min-height: 42px;
    width: 100%;
  }
}