:root {
  color-scheme: light;
  --ink: #172026;
  --muted: #66737d;
  --line: #d8e0e5;
  --paper: #ffffff;
  --wash: #f4f7f8;
  --teal: #087f7a;
  --amber: #a96900;
  --red: #b42318;
}

html[data-theme="dark"] {
  color-scheme: dark;
  --ink: #e6eef2;
  --muted: #a8b7c0;
  --line: #2f414c;
  --paper: #16232c;
  --wash: #101820;
  --teal: #34b8ad;
  --amber: #e4ad4d;
  --red: #ff7b72;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--wash);
  color: var(--ink);
  font-family: Inter, "Segoe UI", "Microsoft YaHei", Arial, sans-serif;
}

.study-sidebar {
  border-right: 1px solid var(--line);
  padding: 20px;
}

.brand {
  align-items: flex-start;
  display: flex;
  gap: 12px;
  justify-content: space-between;
  margin-bottom: 24px;
}

.brand h1 {
  font-size: 22px;
  font-weight: 750;
  letter-spacing: 0;
  line-height: 1.2;
  margin: 4px 0 0;
}

.brand-kicker {
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
}

.mode-toggle {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  margin: 14px 0;
  width: 100%;
}

.mode-toggle .v-btn {
  min-width: 0;
}

.study-sidebar .v-select,
.study-sidebar .v-text-field {
  margin-bottom: 14px;
}

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

.metric {
  background: color-mix(in srgb, var(--teal) 9%, var(--paper));
  border: 1px solid var(--line);
  border-radius: 8px;
  min-height: 72px;
  padding: 12px;
}

.metric span {
  display: block;
  font-size: 24px;
  font-weight: 800;
  line-height: 1;
}

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

.topbar {
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 3;
}

.sidebar-actions {
  display: grid;
  gap: 10px;
  margin-top: 14px;
}

.topbar .v-toolbar-title__placeholder {
  align-items: center;
  display: flex;
  gap: 10px;
  overflow: visible;
}

.content-shell {
  margin: 0 auto;
  max-width: 1180px;
  padding: 22px;
}

.mobile-filters {
  display: none;
}

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

.summary-strip strong {
  display: block;
  font-size: 18px;
  line-height: 1.3;
}

.summary-strip span {
  color: var(--muted);
  display: block;
  font-size: 13px;
  margin-top: 4px;
}

.question-stack {
  display: grid;
  gap: 16px;
}

.question-card {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 18px;
}

.question-card header,
.question-card footer {
  align-items: center;
  display: flex;
  gap: 12px;
  justify-content: space-between;
}

.question-card header > div:first-child {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.card-actions {
  display: flex;
  gap: 2px;
}

.stem {
  color: var(--ink);
  font-size: 15px;
  line-height: 1.62;
  margin: 16px 0;
  white-space: pre-wrap;
}

.choice-group {
  display: grid;
  gap: 8px;
}

.choice-group .v-selection-control {
  align-items: flex-start;
  border: 1px solid var(--line);
  border-radius: 8px;
  min-height: 54px;
  padding: 8px 12px;
}

.choice-group .v-label {
  align-items: flex-start;
  color: var(--ink);
  display: flex;
  gap: 10px;
  opacity: 1;
  width: 100%;
}

.choice-key {
  align-items: center;
  background: color-mix(in srgb, var(--muted) 15%, var(--paper));
  border-radius: 6px;
  display: inline-flex;
  flex: 0 0 28px;
  font-weight: 800;
  height: 28px;
  justify-content: center;
}

.choice-text {
  line-height: 1.55;
  min-width: 0;
  white-space: pre-wrap;
}

.choice-correct {
  border-color: #41a089 !important;
  background: color-mix(in srgb, var(--teal) 14%, var(--paper));
}

.choice-wrong {
  border-color: #da6b61 !important;
  background: color-mix(in srgb, var(--red) 12%, var(--paper));
}

.answer-line {
  align-items: center;
  color: var(--muted);
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  min-width: 0;
}

.explanation {
  background: color-mix(in srgb, var(--teal) 7%, var(--paper));
  border-left: 4px solid var(--teal);
  color: var(--ink);
  line-height: 1.62;
  margin-top: 14px;
  padding: 14px;
  white-space: pre-wrap;
}

.explanation-lock {
  align-items: center;
  background: color-mix(in srgb, var(--amber) 10%, var(--paper));
  border: 1px solid color-mix(in srgb, var(--amber) 35%, var(--line));
  border-radius: 8px;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 12px;
  padding: 10px;
  white-space: normal;
}

.explanation-lock span {
  color: var(--ink);
  flex: 1 1 180px;
}

.ad-slot {
  align-items: center;
  background: color-mix(in srgb, var(--muted) 5%, var(--paper));
  border: 1px dashed #bdc9cf;
  border-radius: 8px;
  color: #7a8790;
  display: flex;
  font-size: 12px;
  justify-content: center;
  min-height: 90px;
}

.ad-slot-top {
  margin-bottom: 16px;
}

.ad-slot-bottom {
  margin-top: 18px;
}

.auth-card .v-card-title {
  font-weight: 750;
}

.account-panel {
  align-items: center;
  background: color-mix(in srgb, var(--teal) 8%, var(--paper));
  border: 1px solid var(--line);
  border-radius: 8px;
  display: flex;
  gap: 12px;
  padding: 14px;
}

.seo-question-page {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 8px;
  line-height: 1.65;
  margin: 24px auto;
  max-width: 980px;
  padding: 24px;
  white-space: normal;
}

.seo-question-page h1,
.seo-question-page h2 {
  line-height: 1.25;
}

.seo-question-page p {
  white-space: pre-wrap;
}

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

.seo-tags span {
  background: color-mix(in srgb, var(--teal) 10%, var(--paper));
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--ink);
  font-size: 12px;
  padding: 3px 8px;
}

.account-panel strong,
.account-panel span {
  display: block;
}

.account-panel span {
  color: var(--muted);
  font-size: 13px;
  margin-top: 3px;
}

@media (max-width: 920px) {
  .mobile-filters {
    display: grid;
    gap: 10px;
    margin-bottom: 14px;
  }

  .mobile-filter-row {
    display: grid;
    gap: 10px;
    grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  }

  .content-shell {
    padding: 14px;
  }

  .topbar .v-toolbar-title {
    flex: 0 1 auto;
    min-width: 0;
  }

  .topbar .v-toolbar-title__placeholder span {
    font-size: 19px;
  }

  .topbar .v-chip {
    display: none;
  }

  .topbar .v-btn {
    width: 38px;
  }

  .summary-strip {
    align-items: flex-start;
    flex-direction: column;
  }

  .question-card {
    padding: 14px;
  }

  .question-card header,
  .question-card footer {
    align-items: flex-start;
    flex-direction: column;
  }

  .ad-slot {
    min-height: 72px;
  }
}