:root {
  /* Core brand palette: blue-first with complementary accents */
  --cts-primary-900: #062a63;
  --cts-primary-700: #0b4db3;
  --cts-primary-600: #1b61c2;
  --cts-primary-500: #2f79d9;
  --cts-primary-100: #eaf2ff;
  --cts-primary-050: #f5f9ff;

  --cts-teal-700: #0f6f80;
  --cts-teal-500: #13a0b4;
  --cts-indigo-700: #5137a8;
  --cts-violet-500: #7a5ce0;
  --cts-amber-700: #8c5a00;

  --cts-success-700: #1e7a3f;
  --cts-danger-700: #a1222e;
  --cts-warning-700: #8a3d00;

  --cts-text-strong: #102a43;
  --cts-text-body: #233548;
  --cts-text-muted: #3d556f;
  --cts-text-subtle: #5f6f85;

  --cts-surface-0: #ffffff;
  --cts-surface-1: #f6f9ff;
  --cts-surface-2: #eef4ff;
  --cts-surface-3: #e2ecff;
  --cts-border-subtle: #c8d8ef;
  --cts-border-default: #adc4e6;

  --cts-focus: #ffbf47;
  --cts-icon-muted: var(--cts-text-muted);
  --cts-icon-success: var(--cts-success-700);
  --cts-icon-warning: var(--cts-danger-700);
  --cts-icon-info: var(--cts-primary-700);
}

body {
  min-height: 100vh;
  color: var(--cts-text-body);
  background: var(--cts-surface-1);
}

a {
  color: var(--cts-primary-700);
}

a:hover,
a:focus-visible {
  color: var(--cts-primary-900);
}

.skip-link {
  position: absolute;
  left: 0.5rem;
  top: -3rem;
  z-index: 1050;
  background: var(--cts-primary-900);
  color: var(--cts-surface-0);
  padding: 0.5rem 0.75rem;
  border-radius: 0.25rem;
}

.skip-link:focus {
  top: 0.5rem;
}

a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible,
[role="button"]:focus-visible {
  outline: 3px solid var(--cts-focus);
  outline-offset: 2px;
}

.feature-card,
.course-card,
.article-card {
  background-color: var(--cts-surface-0);
}

.icon-decorative {
  color: var(--cts-icon-muted);
}

.icon-heading {
  color: var(--cts-icon-info);
}

.icon-status-success {
  color: var(--cts-icon-success);
}

.icon-status-warning {
  color: var(--cts-icon-warning);
}

.icon-status-info {
  color: var(--cts-icon-info);
}

.article-details summary {
  cursor: pointer;
  color: var(--cts-primary-700);
  font-weight: 700;
}

/* -------------------------------------------------------
   Blog-style article post page
------------------------------------------------------- */
.article-post {
  max-width: 780px;
  margin-inline: auto;
}

.article-post-header {
  padding-bottom: 1.75rem;
  margin-bottom: 2rem;
  border-bottom: 2px solid var(--cts-border-subtle);
}

.article-post-title {
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  font-weight: 800;
  color: var(--cts-text-strong);
  line-height: 1.25;
  margin-bottom: 0.85rem;
}

.article-post-summary {
  font-size: 1.2rem;
  line-height: 1.65;
  color: var(--cts-text-muted);
  margin-bottom: 1.25rem;
}

.article-post-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  color: var(--cts-text-subtle);
  font-size: 0.88rem;
}

.article-post-body {
  font-size: 1.08rem;
  line-height: 1.82;
  color: var(--cts-text-body);
}

.article-post-paragraph {
  margin-bottom: 1.4rem;
}

.article-post-footer {
  margin-top: 3rem;
}

/* Key takeaways callout */
.article-key-points {
  border-left: 4px solid var(--cts-primary-600);
  border-radius: 0.75rem;
  background: var(--cts-primary-050);
  padding: 1.25rem 1.5rem;
  margin-bottom: 2rem;
}

.article-key-points-heading {
  font-size: 0.95rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--cts-primary-700);
  margin-bottom: 0.75rem;
}

.article-key-points-list {
  margin: 0;
  padding-left: 1.25rem;
}

.article-key-points-item {
  font-size: 1rem;
  line-height: 1.65;
  color: var(--cts-text-body);
  margin-bottom: 0.35rem;
}

.article-key-points-item:last-child {
  margin-bottom: 0;
}

@media (prefers-reduced-motion: no-preference) {
  .article-post.animate__animated {
    animation-duration: 350ms;
  }
}

.article-rich-body {
  border-left: 0.35rem solid var(--cts-primary-700);
  border-radius: 0.85rem;
  padding: 1rem;
  background: var(--cts-primary-050);
  color: var(--cts-text-body);
}

.article-rich-body p {
  line-height: 1.7;
}

.article-formula-card,
.article-diagram-card {
  border: 1px solid var(--cts-border-default);
  border-radius: 1rem;
  padding: 1rem;
  margin-top: 1rem;
  background: var(--cts-surface-0);
  box-shadow: 0 0.5rem 1.25rem color-mix(in srgb, var(--cts-primary-900) 6%, transparent);
}

.article-formula {
  overflow-x: auto;
  padding: 0.75rem;
  margin-bottom: 0.75rem;
  border-radius: 0.65rem;
  background: var(--cts-surface-2);
}

.article-diagram-title {
  color: var(--cts-primary-900);
  font-weight: 800;
  margin-bottom: 0.25rem;
}

.article-diagram-description {
  color: var(--cts-text-subtle);
  font-size: 0.94rem;
  margin-bottom: 0.75rem;
}

.article-diagram-card .mermaid {
  display: flex;
  justify-content: center;
  overflow-x: auto;
  margin-bottom: 0;
  padding: 0.5rem;
}

.article-diagram-card svg {
  max-width: 100%;
  height: auto;
}

#suggestion-list button {
  margin: 0.125rem;
}

#related-concepts button {
  border: 1px solid var(--cts-text-muted);
}

.course-stage {
  min-height: 28rem;
  overflow: hidden;
  border: 0;
  background:
    radial-gradient(circle at top left, color-mix(in srgb, var(--cts-primary-500) 24%, transparent), transparent 34rem),
    linear-gradient(135deg, var(--cts-surface-0) 0%, var(--cts-primary-050) 100%);
}

.course-stage:fullscreen {
  width: 100vw;
  height: 100vh;
  display: flex;
  flex-direction: column;
  border-radius: 0;
}

.course-stage:fullscreen .card-body {
  flex: 1 1 auto;
  min-height: 0;
  overflow-y: auto;
  overscroll-behavior: contain;
  -webkit-overflow-scrolling: touch;
}

.course-stage:fullscreen .card-footer {
  flex: 0 0 auto;
}

.course-stage:fullscreen .lesson-slide,
.course-stage:fullscreen .quiz-slide,
.course-stage:fullscreen .wizard-gate {
  max-width: 72rem;
  margin-inline: auto;
}

.slide-media {
  max-height: 320px;
  object-fit: cover;
  width: 100%;
}

.course-iframe-wrap {
  border: 1px solid var(--cts-border-default);
  border-radius: 0.75rem;
  overflow: hidden;
  background: var(--cts-surface-2);
}

.course-iframe {
  display: block;
  width: 100%;
  height: 420px;
  border: none;
}

.course-iframe-caption {
  margin: 0;
  padding: 0.5rem 0.75rem;
  font-size: 0.85rem;
  color: var(--cts-text-subtle);
  border-top: 1px solid var(--cts-border-subtle);
  background: var(--cts-surface-1);
}

.lesson-latex {
  border: 1px solid color-mix(in srgb, var(--cts-primary-500) 26%, transparent);
  border-radius: 1rem;
  padding: 1rem 1.25rem;
  background: linear-gradient(135deg, var(--cts-surface-0), var(--cts-primary-050));
}

.lesson-latex-title {
  color: var(--cts-primary-900);
  font-weight: 800;
  margin-bottom: 0.75rem;
}

.lesson-latex-block {
  margin-bottom: 1rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--cts-border-subtle);
}

.lesson-latex-block:last-child {
  margin-bottom: 0;
  padding-bottom: 0;
  border-bottom: none;
}

.lesson-latex-label {
  font-size: 0.82rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--cts-text-subtle);
  margin-bottom: 0.4rem;
}

.lesson-latex-formula {
  overflow-x: auto;
  padding: 0.5rem 0;
}

.lesson-latex-result {
  margin: 0.5rem 0 0;
  font-size: 0.94rem;
  color: var(--cts-text-muted);
  font-style: italic;
}

#activity-canvas {
  width: 100%;
  border: 1px solid var(--cts-border-default);
  border-radius: 0.25rem;
}

footer.site-footer {
  border-top: 1px solid var(--cts-border-subtle);
}

.lesson-slide,
.quiz-slide {
  border-radius: 1rem;
  padding: clamp(1rem, 2vw, 1.75rem);
  border: 1px solid color-mix(in srgb, var(--cts-primary-500) 24%, transparent);
  background: color-mix(in srgb, var(--cts-surface-0) 92%, transparent);
  box-shadow: 0 1rem 2.5rem color-mix(in srgb, var(--cts-primary-900) 8%, transparent);
}

.lesson-hero {
  display: flex;
  gap: 1rem;
  align-items: center;
  margin-bottom: 1rem;
}

.lesson-icon-wrap {
  display: grid;
  place-items: center;
  flex: 0 0 3.5rem;
  width: 3.5rem;
  height: 3.5rem;
  border-radius: 1rem;
  color: var(--cts-surface-0);
  background: linear-gradient(135deg, var(--cts-primary-700), var(--cts-indigo-700));
  box-shadow: 0 0.75rem 1.5rem color-mix(in srgb, var(--cts-primary-700) 28%, transparent);
  font-size: 1.45rem;
}

.lesson-kicker {
  color: var(--cts-text-subtle);
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.lesson-lead {
  margin-bottom: 1rem;
  padding: 1rem;
  border-left: 0.35rem solid var(--cts-primary-700);
  border-radius: 0.75rem;
  background: var(--cts-primary-100);
  color: var(--cts-text-strong);
  font-size: 1.08rem;
  font-weight: 600;
  line-height: 1.65;
}

.lesson-text {
  color: var(--cts-text-body);
  font-size: 1.02rem;
  line-height: 1.72;
}

.lesson-chip {
  border: 1px solid color-mix(in srgb, var(--cts-primary-500) 30%, transparent);
  border-radius: 999px;
  padding: 0.35rem 0.7rem;
  background: var(--cts-primary-050);
  color: var(--cts-primary-900);
  font-size: 0.92rem;
  font-weight: 700;
}

.lesson-source {
  border-left: 0.35rem solid var(--cts-text-muted);
  border-radius: 0.75rem;
  padding: 0.9rem 1rem;
  background: var(--cts-surface-1);
  color: var(--cts-text-body);
  font-size: 0.94rem;
  line-height: 1.6;
}

.lesson-mermaid {
  border: 1px solid color-mix(in srgb, var(--cts-primary-500) 26%, transparent);
  border-radius: 1rem;
  padding: 1rem;
  background: linear-gradient(135deg, var(--cts-surface-0), var(--cts-primary-050));
  box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--cts-surface-0) 75%, transparent);
}

.lesson-mermaid-title {
  color: var(--cts-primary-900);
  font-weight: 800;
  margin-bottom: 0.25rem;
}

.lesson-mermaid-description {
  color: var(--cts-text-subtle);
  font-size: 0.94rem;
  margin-bottom: 0.75rem;
}

.lesson-mermaid .mermaid {
  display: flex;
  justify-content: center;
  overflow-x: auto;
  margin-bottom: 0;
  padding: 0.5rem;
}

.lesson-mermaid svg {
  max-width: 100%;
  height: auto;
}

.lesson-theme-warning .lesson-icon-wrap {
  background: linear-gradient(135deg, var(--cts-danger-700), var(--cts-amber-700));
}

.lesson-theme-warning .lesson-lead {
  border-left-color: var(--cts-danger-700);
  background: color-mix(in srgb, var(--cts-danger-700) 10%, var(--cts-surface-0));
}

.lesson-theme-success .lesson-icon-wrap {
  background: linear-gradient(135deg, var(--cts-success-700), var(--cts-teal-500));
}

.lesson-theme-success .lesson-lead {
  border-left-color: var(--cts-success-700);
  background: color-mix(in srgb, var(--cts-success-700) 10%, var(--cts-surface-0));
}

.lesson-theme-aqua .lesson-icon-wrap {
  background: linear-gradient(135deg, var(--cts-teal-500), var(--cts-primary-700));
}

.lesson-theme-aqua .lesson-lead {
  border-left-color: var(--cts-teal-700);
  background: color-mix(in srgb, var(--cts-teal-500) 10%, var(--cts-surface-0));
}

.lesson-theme-purple .lesson-icon-wrap {
  background: linear-gradient(135deg, var(--cts-indigo-700), var(--cts-violet-500));
}

.lesson-theme-purple .lesson-lead {
  border-left-color: var(--cts-indigo-700);
  background: color-mix(in srgb, var(--cts-violet-500) 10%, var(--cts-surface-0));
}

.quiz-hero .lesson-icon-wrap {
  background: linear-gradient(135deg, var(--cts-primary-700), var(--cts-teal-500));
}

.quiz-question {
  border-radius: 0.75rem;
  padding: 1rem;
  background: var(--cts-primary-100);
  color: var(--cts-text-strong);
  font-size: 1.08rem;
  font-weight: 700;
}

.quiz-option-card {
  border: 1px solid var(--cts-border-default);
  border-radius: 0.75rem;
  padding: 0.85rem 0.85rem 0.85rem 2.4rem;
  background: var(--cts-surface-0);
  transition: border-color 160ms ease, box-shadow 160ms ease, transform 160ms ease;
}

.quiz-option-card:focus-within,
.quiz-option-card:hover {
  border-color: var(--cts-primary-700);
  box-shadow: 0 0.5rem 1.25rem color-mix(in srgb, var(--cts-primary-700) 14%, transparent);
  transform: translateY(-1px);
}

.wizard-gate {
  border: 1px solid color-mix(in srgb, var(--cts-primary-500) 26%, transparent);
  border-left: 0.35rem solid var(--cts-primary-700);
  border-radius: 1rem;
  padding: clamp(1rem, 2vw, 1.5rem);
  background: color-mix(in srgb, var(--cts-surface-0) 94%, transparent);
  box-shadow: 0 1rem 2.5rem color-mix(in srgb, var(--cts-primary-900) 8%, transparent);
}

.wizard-gate-badge {
  font-size: 0.8rem;
  padding: 0.35em 0.65em;
}

.wizard-gate fieldset {
  border: none;
  padding: 0;
  margin: 0;
}

.wizard-gate fieldset legend {
  float: none;
  font-size: 1rem;
}

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