.language-flag {
  width: 21px;
  height: 14px;
  display: block;
  border-radius: 3px;
  box-shadow: 0 0 0 1px #00000012;
  flex-shrink: 0;
}
.theme-toggle {
  width: 34px;
  height: 34px;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--muted);
  border-radius: 50%;
  display: grid;
  place-items: center;
}
.subject-picker {
  position: relative;
  margin-bottom: 16px;
}
.subject-picker summary {
  list-style: none;
  display: flex;
  align-items: center;
  gap: 11px;
  padding: 13px 11px;
  border: 1px solid var(--line);
  background: var(--surface);
  border-radius: 12px;
  cursor: pointer;
  box-shadow: var(--shadow);
}
.subject-picker summary::-webkit-details-marker {
  display: none;
}
.subject-picker summary > span:nth-child(2) {
  min-width: 0;
  flex: 1;
}
.subject-picker summary strong {
  display: block;
  line-height: 1.4;
  font-size: 13px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.subject-picker summary small {
  font-size: 10px;
  color: var(--muted);
  letter-spacing: 0.12em;
}
.subject-picker summary > .icon {
  width: 14px;
  transform: rotate(90deg);
  transition: transform 0.2s;
}
.subject-picker[open] summary > .icon {
  transform: rotate(-90deg);
}
.picker-icon {
  color: var(--accent);
  display: flex;
}
.picker-icon .icon {
  width: 21px;
}
.subject-popover {
  position: absolute;
  top: calc(100% + 8px);
  left: 0;
  width: 310px;
  max-width: calc(100vw - 34px);
  z-index: 50;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 15px;
  box-shadow: 0 16px 46px #14132924;
  padding: 8px;
  max-height: 65vh;
  overflow: auto;
}
.picker-explore {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 12px;
  color: var(--accent);
  padding: 11px;
  border-bottom: 1px solid var(--line);
}
.picker-area > p {
  font-size: 10px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  padding: 12px 10px 6px;
}
.picker-area > a {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 11px 9px;
  border-radius: 9px;
  font-size: 13px;
}
.picker-area > a:hover,
.picker-area > a[aria-current] {
  background: var(--accent-soft);
}
.picker-area > a > span:nth-child(2) {
  flex: 1;
}
.picker-area small {
  display: block;
  font-size: 11px;
  color: var(--muted);
  margin-top: 3px;
}
.picker-course-icon {
  width: 33px;
  height: 33px;
  display: grid;
  place-items: center;
  border-radius: 9px;
  color: var(--course);
  background: color-mix(in srgb, var(--course) 12%, transparent);
}
.picker-course-icon .icon {
  width: 18px;
}
.picker-check {
  color: var(--accent);
}
.picker-check .icon {
  width: 15px;
}
.subject-nav-tree {
  margin: 5px 0 7px 19px;
  padding-left: 12px;
  position: relative;
  border-left: 1px solid var(--line);
}
.subject-nav-tree a {
  font-size: 12px;
  position: relative;
  margin: 2px 0;
}
.subject-nav-tree a::before {
  content: "";
  position: absolute;
  left: -12px;
  top: 50%;
  width: 9px;
  border-top: 1px solid var(--line);
}
.subject-nav-tree .icon {
  width: 16px;
  height: 16px;
}
.privacy-layout {
  max-width: 850px;
}
.privacy-layout .aside-card {
  margin-top: 20px;
}
.privacy-layout h2 {
  margin-bottom: 12px;
}
.privacy-layout p + p {
  margin-top: 12px;
}
.privacy-layout a {
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 3px;
}
.privacy-layout ul {
  color: var(--muted);
  padding-left: 22px;
}
.privacy-settings {
  margin-top: 26px;
}
.privacy-settings > label {
  display: flex;
  gap: 12px;
  align-items: flex-start;
}
.privacy-settings input {
  margin-top: 6px;
  accent-color: var(--accent);
  width: 18px;
  height: 18px;
}
.privacy-settings small {
  display: block;
  color: var(--muted);
  font-size: 13px;
  margin-top: 6px;
}
.privacy-settings .button-row {
  margin-top: 16px;
}
.analytics-status {
  font-size: 12px;
  margin-top: 12px;
  color: var(--muted);
}
:root[data-theme="dark"] {
  --bg: #121521;
  --surface: #1a1f30;
  --ink: #edf0fa;
  --muted: #a9b1c8;
  --accent: #a49aff;
  --accent-soft: #2a2546;
  --line: #30384d;
  --shadow: 0 8px 24px #00000012;
  --green: #a9db73;
  color-scheme: dark;
}
[data-theme="dark"] .sidebar,
[data-theme="dark"] .topbar,
[data-theme="dark"] .site-footer {
  background: var(--surface);
  border-color: var(--line);
}
[data-theme="dark"] .language-toggle {
  background: var(--bg);
}
[data-theme="dark"] .language-toggle button[aria-pressed="true"] {
  background: var(--surface);
}
[data-theme="dark"] .language-toggle button,
[data-theme="dark"] input,
[data-theme="dark"] select,
[data-theme="dark"] textarea {
  color: var(--ink);
}
[data-theme="dark"] .catalog-search,
[data-theme="dark"] .enroll-button,
[data-theme="dark"] .area-filters button,
[data-theme="dark"] .profile-input,
[data-theme="dark"] .profile-choice,
[data-theme="dark"] .challenge textarea {
  background: var(--surface);
}
[data-theme="dark"] .empty-state {
  background: var(--accent-soft);
  border-color: var(--line);
}
[data-theme="dark"] .button {
  background: var(--surface);
  color: var(--ink);
  border-color: var(--line);
}
[data-theme="dark"] .button.primary {
  background: #7161ec;
  color: white;
  border-color: #7161ec;
}
[data-theme="dark"] .topic-card,
[data-theme="dark"] .lesson-card,
[data-theme="dark"] .aside-card,
[data-theme="dark"] .experiment-card,
[data-theme="dark"] .reading-card,
[data-theme="dark"] .lab-stage,
[data-theme="dark"] .trace-frame,
[data-theme="dark"] .challenge,
[data-theme="dark"] .worked-example,
[data-theme="dark"] .quiz-card {
  background: var(--surface);
  border-color: var(--line);
}
[data-theme="dark"] .hero,
[data-theme="dark"] .visual-hero {
  background: linear-gradient(135deg, #242540, #1b2336);
}
[data-theme="dark"] .topic-symbol {
  background: color-mix(in srgb, var(--topic) 15%, var(--surface));
}
[data-theme="dark"] .data-table th,
[data-theme="dark"] .data-table td {
  border-color: var(--line);
}
[data-theme="dark"] .data-table th {
  background: var(--bg);
}
[data-theme="dark"] .formula,
[data-theme="dark"] .reading-formula,
[data-theme="dark"] pre,
[data-theme="dark"] .code-block {
  background: #111522;
  color: #e0ddff;
}
[data-theme="dark"] .tabs,
[data-theme="dark"] .lesson-tabs,
[data-theme="dark"] .simulation-toolbar,
[data-theme="dark"] .trace-controls {
  background: var(--surface);
  border-color: var(--line);
}
[data-theme="dark"] .simulation-stage,
[data-theme="dark"] .experiment-stage {
  background: #171b2a;
}
[data-theme="dark"] .storage-note {
  background: #453822;
  color: #f5d4a0;
}
[data-theme="dark"] .skip-link {
  background: var(--surface);
}
[data-theme="dark"] #toast {
  background: #edeaff;
  color: #202334;
}
[data-theme="dark"] .primary-nav a:hover,
[data-theme="dark"] .topic-nav a:hover {
  background: var(--accent-soft);
}
.sidebar .subject-popover {
  width: 100%;
  max-width: none;
}
.sidebar .picker-area > a {
  padding: 10px 7px;
  gap: 8px;
}
.sidebar .picker-area small {
  font-size: 10px;
}
.sidebar .picker-course-icon {
  width: 28px;
  height: 28px;
  flex-shrink: 0;
}
[data-theme="dark"] .progress-track,
[data-theme="dark"] .sidebar-progress {
  background: #30384d;
}
.topic-card,
.card-body,
.topic-nav a {
  min-width: 0;
  overflow-wrap: anywhere;
}
[data-theme="dark"] .resume-banner,
[data-theme="dark"] .reading-section,
[data-theme="dark"] .exercise-card,
[data-theme="dark"] .hint,
[data-theme="dark"] .quiz-question,
[data-theme="dark"] .lab-card {
  background: var(--surface);
  border-color: var(--line);
}
[data-theme="dark"] .trace-view,
[data-theme="dark"] .trace-note,
[data-theme="dark"] .source-note,
[data-theme="dark"] .simulation-controls,
[data-theme="dark"] .lab-controls,
[data-theme="dark"] .lab-summary,
[data-theme="dark"] .lab-figure,
[data-theme="dark"] .simulation-log {
  background: var(--bg);
  border-color: var(--line);
}
[data-theme="dark"] .answer-box,
[data-theme="dark"] .self-check,
[data-theme="dark"] .simulation-challenge {
  background: var(--accent-soft);
  border-color: var(--line);
}
[data-theme="dark"] .lab-button,
[data-theme="dark"] .quiz-option {
  background: var(--surface);
  color: var(--ink);
  border-color: var(--line);
}
[data-theme="dark"] .dl-figure,
[data-theme="dark"] .dl-panel {
  background: var(--surface);
}
[data-theme="dark"] .dl-metric,
[data-theme="dark"] .dl-case-list span,
[data-theme="dark"] .dl-bar {
  background: var(--bg);
}
[data-theme="dark"] .dl-prediction {
  background: var(--accent-soft);
  border-color: var(--line);
}
[data-theme="dark"] .dl-prediction .pill {
  background: var(--surface);
}
[data-theme="dark"] .dl-figure svg text {
  fill: var(--muted);
}
[data-theme="dark"] .dl-grid {
  stroke: #30384d;
}
[data-theme="dark"] .dl-contour {
  stroke: #48516b;
}
[data-theme="dark"] .dl-node circle {
  fill: var(--surface);
  stroke: #59627d;
}
[data-theme="dark"] .dl-node.active circle {
  fill: #3f355e;
  stroke: #b19aff;
}
[data-theme="dark"] .dl-node text {
  fill: var(--ink);
}
[data-theme="dark"] .dl-confusion .good {
  background: #203e36;
}
[data-theme="dark"] .dl-confusion .bad {
  background: #482b38;
}
@media (max-width: 650px) {
  .topbar-tools {
    gap: 7px;
  }
  .profile-link > span:last-child {
    display: none;
  }
  .language-toggle button {
    padding: 4px 6px;
  }
  .theme-toggle {
    width: 30px;
    height: 30px;
  }
  .privacy-layout {
    padding: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

/* Shared study components keep the same semantic states in both themes. */
[data-theme="dark"]
  :is(
    .learning-tabs,
    .learning-content,
    .plan-summary,
    .method-card,
    .plan-topic,
    .practice-sheet,
    .exam-setup,
    .reading-figure,
    .field,
    textarea,
    .icon-button
  ) {
  background: var(--surface);
  border-color: var(--line);
  color: var(--ink);
}
[data-theme="dark"]
  :is(.lesson-summary, .reflection, .sheet-header, .option-letter) {
  background: var(--accent-soft);
  border-color: var(--line);
}
[data-theme="dark"]
  :is(
    .reading-section > p,
    .reading-bullets,
    .exercise-prompt,
    .solution-steps p,
    .hint p,
    .field-label,
    .lesson-summary p,
    td
  ) {
  color: var(--muted);
}
[data-theme="dark"] .quiz-question legend {
  color: var(--ink);
}
[data-theme="dark"] .option-letter {
  color: var(--accent);
}
[data-theme="dark"] th {
  background: var(--bg);
  color: var(--ink);
}
[data-theme="dark"] .quiz-option:hover {
  background: var(--accent-soft);
  border-color: var(--accent);
}
[data-theme="dark"]
  :is(.quiz-option.correct, .feedback.success, .button.completed, .answer-box) {
  background: #203e36;
  color: #a6e5ca;
  border-color: #437d68;
}
[data-theme="dark"] .quiz-option.correct .option-letter {
  background: #31584b;
  color: #b5f0d8;
}
[data-theme="dark"] .quiz-option.incorrect {
  background: #482b38;
  color: #ffd0dc;
  border-color: #a76980;
}
[data-theme="dark"] .quiz-option.incorrect .option-letter {
  background: #623749;
  color: #ffd0dc;
}
[data-theme="dark"] .feedback.retry {
  background: #443224;
  color: #f3c390;
}
[data-theme="dark"] :is(.example-label, .worked-disclosure summary) {
  color: #8edbbb;
}
[data-theme="dark"] .enrollment-list label {
  background: var(--bg);
  color: var(--ink);
}
[data-theme="dark"] .lab-choice {
  background: var(--surface);
  color: var(--muted);
  border-color: var(--line);
}
[data-theme="dark"] .lab-choice.active,
[data-theme="dark"] .lab-choice:hover {
  background: var(--accent-soft);
  color: var(--accent);
  border-color: var(--accent);
}
[data-theme="dark"] .pill {
  background: var(--accent-soft);
  color: var(--muted);
}