/**
 * Electricity & Magnetism — interactive course
 * Uses site tokens from base.css / theme.css; Ratio accent.
 */

.home-em-course,
.em-course-root {
  --em-accent: var(--ratio-accent);
  --em-space-1: 0.5rem;
  --em-space-2: 0.75rem;
  --em-space-3: 1rem;
  --em-space-4: 1.25rem;
  --em-space-5: 1.5rem;
  --em-space-6: 2rem;
  --em-space-7: 2.5rem;
}

/* ——— Home strip ——— */

.home-em-course {
  margin: 0 auto;
  padding: var(--em-space-7) 0 0;
  width: 100%;
  max-width: var(--max-width);
  border-top: 1px solid var(--color-panel-outline);
}

.home-em-course__header {
  margin-bottom: var(--em-space-5);
}

.home-em-course__header h2 {
  margin: 0 0 var(--em-space-2);
  font-family: var(--font-serif);
  font-size: clamp(1.35rem, 3vw, 1.75rem);
  font-weight: 500;
  color: var(--color-text);
}

.home-em-course__header p {
  margin: 0;
  max-width: 58ch;
  color: var(--color-muted);
  font-size: 0.95rem;
  line-height: 1.55;
}

.home-em-course__embed {
  border: 1px solid var(--color-panel-outline);
  border-radius: 0.85rem;
  background: var(--color-surface);
  padding: var(--em-space-5) var(--em-space-6);
  box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--color-text) 2.5%, transparent);
}

@media (max-width: 36rem) {
  .home-em-course__embed {
    padding: var(--em-space-4);
  }
}

/* ——— Course shell ——— */

.em-course {
  --em-accent: var(--ratio-accent);
  color: var(--color-text);
  font-family: var(--font-sans);
}

.em-course__eyebrow {
  margin: 0 0 var(--em-space-2);
  font-size: 0.85rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-muted);
}

.em-course__title {
  margin: 0 0 var(--em-space-2);
  font-family: var(--font-serif);
  font-size: clamp(1.35rem, 3vw, 1.65rem);
  font-weight: 500;
  line-height: 1.2;
}

.em-course__subtitle {
  margin: 0;
  max-width: 52ch;
  color: var(--color-muted);
  font-size: 0.95rem;
  line-height: 1.55;
}

.em-course__layers {
  display: flex;
  flex-wrap: wrap;
  gap: var(--em-space-2);
  margin: var(--em-space-5) 0 var(--em-space-4);
}

.em-layer-pill {
  font-size: 0.78rem;
  padding: 0.25rem 0.65rem;
  border-radius: 999px;
  border: 1px solid color-mix(in srgb, var(--em-accent) 35%, var(--color-panel-outline));
  background: color-mix(in srgb, var(--em-accent) 8%, var(--color-surface));
  color: var(--color-text);
}

.em-course__progress {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--em-space-3);
  margin-bottom: var(--em-space-5);
}

.em-course__progress--inline {
  margin-bottom: 0;
  flex: 1;
  min-width: 12rem;
}

.em-course__progress-bar {
  flex: 1;
  min-width: 8rem;
  max-width: 16rem;
  height: 0.35rem;
  border-radius: 999px;
  background: color-mix(in srgb, var(--color-text) 10%, transparent);
  overflow: hidden;
}

.em-course__progress-fill {
  display: block;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(
    90deg,
    color-mix(in srgb, var(--em-accent) 70%, transparent),
    var(--em-accent)
  );
  transition: width 280ms ease;
}

.em-course__progress-label {
  font-size: 0.85rem;
  color: var(--color-muted);
  white-space: nowrap;
}

.em-course__home-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--em-space-2) var(--em-space-3);
  margin-top: var(--em-space-5);
  padding-top: var(--em-space-4);
  border-top: 1px solid var(--color-panel-outline);
}

.em-course__full-link {
  margin-left: auto;
}

@media (max-width: 40rem) {
  .em-course__full-link {
    margin-left: 0;
    width: 100%;
  }
}

.em-course__home-preview .em-lesson-panel {
  border: none;
  padding: 0;
  box-shadow: none;
  background: transparent;
}

.em-course__home-preview .em-lesson-panel__body {
  max-height: 22rem;
  overflow: auto;
  padding-right: var(--em-space-2);
  scrollbar-width: thin;
}

/* ——— Full layout ——— */

.em-course--full {
  display: grid;
  grid-template-columns: minmax(11rem, 15rem) minmax(0, 1fr);
  gap: var(--em-space-5) var(--em-space-6);
  align-items: start;
  width: 100%;
}

.em-main {
  min-width: 0;
}

.em-panels .em-lesson-panel {
  max-width: 100%;
}

@media (max-width: 900px) {
  .em-course--full {
    grid-template-columns: 1fr;
  }
}

.em-sidebar {
  position: sticky;
  top: var(--em-space-4);
  max-height: calc(100vh - 6rem);
  overflow: auto;
  padding: var(--em-space-4);
  border: 1px solid var(--color-panel-outline);
  border-radius: 0.85rem;
  background: var(--color-surface);
  scrollbar-width: thin;
}

@media (max-width: 900px) {
  .em-sidebar {
    position: static;
    max-height: 14rem;
  }
}

.em-sidebar__label {
  margin: 0 0 var(--em-space-3);
  font-size: 0.8rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-muted);
}

.em-toc {
  display: flex;
  flex-direction: column;
  gap: 0.15rem;
}

.em-toc-part {
  margin: var(--em-space-3) 0 var(--em-space-1);
  font-size: 0.72rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: color-mix(in srgb, var(--em-accent) 75%, var(--color-muted));
}

.em-toc-part:first-child {
  margin-top: 0;
}

.em-toc-link {
  display: block;
  width: 100%;
  text-align: left;
  font-family: var(--font-sans);
  font-size: 0.82rem;
  line-height: 1.35;
  padding: 0.45rem 0.55rem;
  border: none;
  border-radius: 0.45rem;
  background: transparent;
  color: var(--color-text);
  cursor: pointer;
  transition: background 150ms ease, color 150ms ease;
}

.em-toc-link:hover,
.em-toc-link:focus-visible {
  background: color-mix(in srgb, var(--em-accent) 12%, transparent);
}

.em-toc-link.is-active {
  background: color-mix(in srgb, var(--em-accent) 18%, transparent);
  font-weight: 600;
}

.em-toc-link.is-done::after {
  content: " ✓";
  opacity: 0.65;
  font-size: 0.75em;
}

.em-toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--em-space-3);
  margin-bottom: var(--em-space-5);
  padding-bottom: var(--em-space-4);
  border-bottom: 1px solid var(--color-panel-outline);
}

.em-toolbar__nav {
  display: flex;
  gap: var(--em-space-2);
}

.em-nav-btn {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  padding: 0.45rem 0.95rem;
  border-radius: 999px;
  border: 1px solid var(--color-panel-outline);
  background: transparent;
  color: var(--color-text);
  cursor: pointer;
  transition: border-color 150ms ease, background 150ms ease;
}

.em-nav-btn:hover:not(:disabled),
.em-nav-btn:focus-visible:not(:disabled) {
  border-color: var(--color-text);
  background: color-mix(in srgb, var(--color-text) 6%, transparent);
}

.em-nav-btn--primary {
  border-color: color-mix(in srgb, var(--em-accent) 50%, var(--color-panel-outline));
  background: color-mix(in srgb, var(--em-accent) 14%, var(--color-surface));
}

.em-nav-btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

/* ——— Lesson panels ——— */

.em-lesson-panel {
  padding: var(--em-space-5) var(--em-space-6);
  border: 1px solid var(--color-panel-outline);
  border-radius: 0.85rem;
  background: var(--color-surface);
  box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--color-text) 2%, transparent);
}

.em-lesson-panel__kicker {
  margin: 0 0 var(--em-space-1);
  font-size: 0.8rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-muted);
}

.em-lesson-panel__title {
  margin: 0 0 var(--em-space-4);
  font-family: var(--font-serif);
  font-size: clamp(1.2rem, 2.5vw, 1.5rem);
  font-weight: 500;
  line-height: 1.25;
}

/* ——— Two-column lesson layout ——— */

.em-lesson-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(260px, 340px);
  gap: var(--em-space-6);
  align-items: start;
}

@media (max-width: 960px) {
  .em-lesson-layout {
    grid-template-columns: 1fr;
  }

  .em-lesson-layout__lab {
    order: -1;
  }
}

.em-lesson-layout__content {
  min-width: 0;
}

.em-lesson-layout__lab {
  position: sticky;
  top: var(--em-space-4);
}

.em-course--home .em-lesson-layout {
  grid-template-columns: 1fr;
}

.em-course--home .em-lesson-layout__lab {
  position: static;
  order: 0;
}

/* ——— Insight card ——— */

.em-insight {
  margin: 0 0 var(--em-space-5);
  padding: var(--em-space-4) var(--em-space-5);
  border-radius: 0.65rem;
  border: 1px solid color-mix(in srgb, var(--em-accent) 35%, var(--color-panel-outline));
  border-inline-start: 3px solid var(--em-accent);
  background: color-mix(in srgb, var(--em-accent) 8%, var(--color-surface));
}

.em-insight__label {
  margin: 0 0 var(--em-space-2);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-muted);
}

.em-insight__text {
  margin: 0;
  font-size: 0.95rem;
  line-height: 1.55;
}

.em-insight__text .katex {
  font-size: 1em;
}

/* ——— Lab panel ——— */

.em-lab-mount,
.em-lab-teaser {
  border: 1px solid var(--color-panel-outline);
  border-radius: 0.75rem;
  background: color-mix(in srgb, var(--color-bg-accent) 50%, var(--color-surface));
  overflow: hidden;
}

.em-lab-teaser {
  padding: var(--em-space-4) var(--em-space-5);
}

.em-lab-teaser__label {
  margin: 0 0 var(--em-space-1);
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-muted);
}

.em-lab-teaser__title {
  margin: 0 0 var(--em-space-2);
  font-weight: 600;
  font-size: 0.95rem;
}

.em-lab-teaser__link {
  font-size: 0.85rem;
  font-weight: 500;
}

.em-lab {
  padding: var(--em-space-4);
}

.em-lab__title {
  margin: 0 0 var(--em-space-3);
  font-size: 0.82rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: color-mix(in srgb, var(--em-accent) 80%, var(--color-text));
}

.em-lab__stage {
  min-height: 8rem;
}

.em-lab-canvas {
  display: block;
  width: 100%;
  max-width: 100%;
  height: auto;
  border-radius: 0.5rem;
  background: var(--color-surface);
  border: 1px solid var(--color-panel-outline);
}

.em-lab-control {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: var(--em-space-2);
  align-items: center;
  margin-bottom: var(--em-space-3);
  font-size: 0.82rem;
}

.em-lab-control label {
  grid-column: 1 / -1;
  color: var(--color-muted);
}

.em-lab-control input[type="range"] {
  grid-column: 1;
  width: 100%;
  accent-color: var(--em-accent);
}

.em-lab-control output {
  font-variant-numeric: tabular-nums;
  color: var(--color-text);
  min-width: 3.5rem;
  text-align: right;
}

.em-lab-readout {
  margin: var(--em-space-3) 0 0;
  font-size: 0.85rem;
  line-height: 1.5;
  color: var(--color-muted);
}

.em-lab-readout .katex {
  font-size: 0.95em;
}

.em-lab-action {
  margin-top: var(--em-space-3);
  font-family: var(--font-sans);
  font-size: 0.85rem;
  padding: 0.45rem 1rem;
  border-radius: 999px;
  border: 1px solid var(--em-accent);
  background: color-mix(in srgb, var(--em-accent) 14%, var(--color-surface));
  color: var(--color-text);
  cursor: pointer;
}

.em-lab-layers {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.em-lab-layer-btn {
  text-align: left;
  padding: 0.5rem 0.65rem;
  border: 1px solid var(--color-panel-outline);
  border-radius: 0.45rem;
  background: var(--color-surface);
  font-family: var(--font-sans);
  font-size: 0.85rem;
  cursor: pointer;
}

.em-lab-layer-btn.is-active {
  border-color: var(--em-accent);
  background: color-mix(in srgb, var(--em-accent) 16%, var(--color-surface));
  font-weight: 600;
}

.em-lab-toggle {
  display: flex;
  gap: var(--em-space-2);
  margin-bottom: var(--em-space-3);
}

.em-lab-toggle-btn {
  flex: 1;
  padding: 0.4rem;
  border-radius: 999px;
  border: 1px solid var(--color-panel-outline);
  background: transparent;
  cursor: pointer;
  font-family: var(--font-sans);
  font-size: 0.85rem;
}

.em-lab-toggle-btn.is-active {
  border-color: var(--em-accent);
  background: color-mix(in srgb, var(--em-accent) 14%, transparent);
}

.em-lab-gauge {
  margin: var(--em-space-3) 0;
}

.em-lab-flow {
  display: block;
  height: 0.5rem;
  margin-top: var(--em-space-2);
  border-radius: 999px;
  background: linear-gradient(90deg, var(--em-accent), color-mix(in srgb, var(--em-accent) 40%, transparent));
  transition: width 200ms ease;
}

.em-lab-power-readout {
  margin: var(--em-space-3) 0 0;
  font-size: 1.25rem;
  font-weight: 600;
  text-align: center;
}

.em-lab-split {
  display: flex;
  height: 2.5rem;
  border-radius: 0.5rem;
  overflow: hidden;
  border: 1px solid var(--color-panel-outline);
}

.em-lab-split__e,
.em-lab-split__b {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 600;
  transition: flex 300ms ease;
}

.em-lab-split__e {
  background: color-mix(in srgb, #c45c5c 25%, var(--color-surface));
}

.em-lab-split__b {
  background: color-mix(in srgb, #4a7eb5 25%, var(--color-surface));
}

.em-lab-network {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.5rem;
}

.em-lab-node {
  padding: 0.55rem;
  border-radius: 0.45rem;
  border: 1px solid var(--color-panel-outline);
  background: var(--color-surface);
  font-size: 0.75rem;
  cursor: pointer;
}

.em-lab-node.is-active {
  border-color: var(--em-accent);
  background: color-mix(in srgb, var(--em-accent) 12%, var(--color-surface));
}

.em-lab-ring {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  justify-content: center;
  padding: var(--em-space-4);
}

.em-lab-ring__seg {
  padding: 0.5rem 0.85rem;
  border-radius: 999px;
  border: 1px solid var(--color-panel-outline);
  font-size: 0.85rem;
  font-weight: 600;
}

.em-lab-synthesis {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  max-height: 220px;
  overflow: auto;
}

.em-lab-syn-btn {
  text-align: left;
  padding: 0.45rem 0.6rem;
  border: 1px solid var(--color-panel-outline);
  border-radius: 0.4rem;
  background: var(--color-surface);
  font-family: var(--font-sans);
  font-size: 0.78rem;
  cursor: pointer;
}

.em-lab-syn-btn.is-active {
  border-color: var(--em-accent);
  background: color-mix(in srgb, var(--em-accent) 12%, var(--color-surface));
}

.em-lesson-panel__body.entry {
  max-width: none;
}

.em-lesson-panel__body p,
.em-lesson-panel__body li {
  line-height: 1.65;
}

.em-section-heading {
  margin: var(--em-space-5) 0 var(--em-space-3);
  font-family: var(--font-serif);
  font-size: 1.1rem;
  font-weight: 500;
}

.em-section-heading:first-child {
  margin-top: 0;
}

.em-equation {
  margin: var(--em-space-4) 0;
  padding: var(--em-space-4) var(--em-space-5);
  overflow-x: auto;
  border-radius: 0.55rem;
  background: color-mix(in srgb, var(--em-accent) 7%, var(--color-bg-accent));
  border: 1px solid color-mix(in srgb, var(--em-accent) 18%, var(--color-panel-outline));
  text-align: center;
}

.em-equation .katex-display {
  margin: 0;
  overflow-x: auto;
  overflow-y: hidden;
}

.em-equation .katex {
  font-size: 1.12em;
}

.em-section-body .katex {
  font-size: 1.02em;
}

.em-section-body li .katex {
  font-size: 1em;
}

.em-quiz__prompt .katex,
.em-quiz__explain .katex {
  font-size: 1em;
}

.em-hr {
  margin: var(--em-space-5) 0;
  border: none;
  border-top: 1px solid var(--color-panel-outline);
}

.em-lesson-panel__footer {
  margin-top: var(--em-space-5);
  padding-top: var(--em-space-4);
  border-top: 1px solid var(--color-panel-outline);
}

.em-mark-read {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  padding: 0.45rem 1rem;
  border-radius: 999px;
  border: 1px solid var(--color-panel-outline);
  background: transparent;
  color: var(--color-text);
  cursor: pointer;
}

.em-mark-read:hover:not(:disabled),
.em-mark-read:focus-visible:not(:disabled) {
  border-color: var(--em-accent);
  background: color-mix(in srgb, var(--em-accent) 10%, transparent);
}

.em-mark-read:disabled {
  opacity: 0.7;
  cursor: default;
}

/* ——— Quiz ——— */

.em-quiz {
  margin-top: var(--em-space-6);
  padding: var(--em-space-4) var(--em-space-5);
  border-radius: 0.65rem;
  border: 1px solid color-mix(in srgb, var(--em-accent) 30%, var(--color-panel-outline));
  background: color-mix(in srgb, var(--em-accent) 5%, var(--color-surface));
}

.em-quiz__prompt {
  margin: 0 0 var(--em-space-3);
  font-weight: 500;
}

.em-quiz__options {
  display: flex;
  flex-direction: column;
  gap: var(--em-space-2);
}

.em-quiz-opt {
  text-align: left;
  font-family: var(--font-sans);
  font-size: 0.9rem;
  padding: 0.55rem 0.85rem;
  border-radius: 0.5rem;
  border: 1px solid var(--color-panel-outline);
  background: var(--color-surface);
  color: var(--color-text);
  cursor: pointer;
  transition: border-color 150ms ease, background 150ms ease;
}

.em-quiz-opt:hover:not(:disabled) {
  border-color: var(--em-accent);
}

.em-quiz-opt.is-correct {
  border-color: #2d8a5e;
  background: color-mix(in srgb, #2d8a5e 12%, var(--color-surface));
}

.em-quiz-opt.is-wrong {
  border-color: #b44;
  background: color-mix(in srgb, #b44 10%, var(--color-surface));
}

.em-quiz__feedback {
  margin: var(--em-space-3) 0 0;
  font-size: 0.9rem;
  font-weight: 500;
}

.em-quiz__explain {
  margin: var(--em-space-2) 0 0;
  font-size: 0.88rem;
  color: var(--color-muted);
  line-height: 1.5;
}

.em-course-error,
.em-course-loading {
  color: var(--color-muted);
  padding: var(--em-space-4);
  font-size: 0.95rem;
}

/* Course page intro */
.page-intro--course {
  max-width: var(--max-width);
  margin-inline: auto;
}

.page-content--course {
  max-width: var(--max-width);
  margin-inline: auto;
}

.header-featured-link--course {
  border-color: color-mix(in srgb, var(--ratio-accent) 45%, var(--color-panel-outline));
  color: var(--color-text);
  font-weight: 500;
}