/* Lesson furniture (Story 1.8): lesson-header, track-contents, lesson-nav.
   Tokens only -- references the custom properties tokens.css.njk already
   emits (same precedent as prose.css); no color, font, or spacing value is
   restated here. */

/* lesson-layout -- two columns at >=1040px: the prose column stays pinned
   at --spacing-measure and track-contents moves into a sidebar rail by
   grid placement only (never DOM reordering -- EXPERIENCE.md:86). The PAGE
   widens (shell.css already caps header/main/footer at --spacing-page-max);
   the column never does (DESIGN.md: "widen the page, not narrow the
   column"). Single column, normal flow below 1040px. */
.lesson-layout {
  display: grid;
  grid-template-columns: minmax(0, var(--spacing-measure)) var(--spacing-sidebar);
  gap: var(--spacing-10);
  align-items: start;
}

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

@media (max-width: 1039px) {
  .lesson-layout {
    grid-template-columns: minmax(0, 1fr);
  }
}

/* lesson-header */
.lesson-header-meta {
  margin: 0 0 var(--spacing-4);
  color: var(--fg-muted);
  font-size: var(--font-meta-size);
  font-weight: var(--font-meta-weight);
  line-height: var(--font-meta-line-height);
}

.lesson-header-rule {
  margin: 0 0 var(--spacing-8);
  border: 0;
  border-top: 1px solid var(--border);
}

/* track-contents -- uncollapsed on every lesson page (EXPERIENCE.md:82),
   always. Rows divided by border-subtle only (deleting the rule loses
   nothing -- layout and link text already separate rows); each row keeps
   a >=24px hit area (NFR20, 2.5.8). */
.track-contents {
  margin-top: var(--spacing-10);
}

.track-contents-heading {
  margin: 0 0 var(--spacing-2);
  font-size: var(--font-h2-size);
  font-weight: var(--font-h2-weight);
  line-height: var(--font-h2-line-height);
}

.track-contents-group-title {
  font-size: var(--font-h3-size);
  font-weight: var(--font-h3-weight);
  line-height: var(--font-h3-line-height);
  margin: var(--spacing-4) 0 var(--spacing-2);
}

.track-contents ol {
  list-style: none;
  margin: 0;
  padding: 0;
  border-top: 1px solid var(--border-subtle);
}

.track-contents li {
  border-bottom: 1px solid var(--border-subtle);
}

.track-contents-row {
  display: flex;
  align-items: baseline;
  gap: var(--spacing-3);
  min-height: 24px;
  padding: var(--spacing-1) 2px;
  font-size: var(--font-meta-size);
  line-height: var(--font-meta-line-height);
  color: var(--fg-muted);
}

.track-contents-row a {
  display: flex;
  flex: 1 1 auto;
  align-items: baseline;
  gap: var(--spacing-3);
  min-height: 24px;
  color: var(--fg-muted);
  text-decoration: none;
}

.track-contents-row a:hover,
.track-contents-row a:focus-visible {
  color: var(--accent);
}

.track-contents-index {
  flex: 0 0 auto;
  color: var(--fg-muted);
  font-variant-numeric: tabular-nums;
}

.track-contents-title {
  flex: 1 1 auto;
}

.track-contents-duration {
  flex: 0 0 auto;
  color: var(--fg-muted);
}

/* Current lesson: unlinked, fg at weight 600, and glyph-marked via a CSS
   ::before (never a duplicated DOM node) -- never color alone. */
.track-contents-row[aria-current="page"] .track-contents-title {
  color: var(--fg);
  font-weight: 600;
}

.track-contents-row[aria-current="page"] .track-contents-index::before {
  content: "\25B8";
  color: var(--accent);
  margin-right: var(--spacing-1);
}

/* >=1040px: 260px sticky right-hand rail with its own border-left rule and
   overflow-y so a long list never exceeds the viewport; durations dropped
   to stay narrow; heading shrinks to an uppercase meta-sized label. */
@media (min-width: 1040px) {
  .lesson-layout .track-contents {
    position: sticky;
    top: var(--spacing-6);
    align-self: start;
    max-height: calc(100vh - var(--spacing-10));
    overflow-y: auto;
    margin-top: 0;
    border-left: 1px solid var(--border);
    padding-left: var(--spacing-5);
  }

  .lesson-layout .track-contents-heading {
    font-size: var(--font-meta-size);
    font-weight: var(--font-meta-weight);
    line-height: var(--font-meta-line-height);
    text-transform: uppercase;
  }

  .lesson-layout .track-contents-duration {
    display: none;
  }
}

/* lesson-nav -- prev / track index / next, above the footer. Prev/next in
   accent, the index link muted as the secondary action (DESIGN.md). */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--spacing-4);
  margin-top: var(--spacing-6);
  padding-top: var(--spacing-3);
  border-top: 1px solid var(--border);
  font-size: var(--font-meta-size);
  line-height: var(--font-meta-line-height);
}

.lesson-nav-prev,
.lesson-nav-next {
  color: var(--accent);
}

.lesson-nav-index {
  color: var(--fg-muted);
}

/* <640px: the three links stack vertically when they cannot fit one line. */
@media (max-width: 639px) {
  .lesson-nav {
    flex-direction: column;
    align-items: flex-start;
    gap: var(--spacing-2);
  }
}

/* print (Story 1.10, NFR43) -- lesson-nav is furniture, dropped like
   site-nav/prompt-path/footer (shell.css). track-contents unsticks back to
   normal flow regardless of viewport width, since print is evaluated
   independently of the 1040px sidebar-rail condition above; every lesson
   stays listed (it is never wrapped in <details>). */
@media print {
  .lesson-nav {
    display: none;
  }

  .track-contents {
    position: static;
    max-height: none;
    overflow-y: visible;
  }
}