/* ═══════════════════════════════════════════════════════════════════════════
   lesson.css — SHARED article (lesson-page) design system
   ---------------------------------------------------------------------------
   The one common article design: solid-ink hero ("Gen A", the wrl101 m1-l1
   standard). Load AFTER theme.css (and after theme-rtl.css on Arabic pages).
   A design change to an article component is made HERE, once — never copied
   into the ~446 article files again.

   What lives WHERE
   - theme.css   : global chrome (navbar, footer, .container, tokens, .fade-up
                   transition + reduced-motion guard) AND `.lesson-hero .breadcrumb`
                   (3 rules). Those breadcrumb rules are deliberately NOT repeated
                   here — theme.css owns them.
   - lesson.css  : article components (this file).
   - per-article : bespoke per-lesson diagrams only (.gen-*, .domain-*, .block-*,
                   .variant-*, .param-*, .choose-*, .power-bar*, .spectrum-table,
                   …) stay INLINE in that article. They are not shared design.

   No hardcoded brand colours — design tokens only (var(--ink) etc.). RTL is
   handled with logical properties (margin-inline / border-inline-start / …),
   so no per-page RTL rule is needed.

   ── Canonical vocabulary (winners), with the legacy alias each replaced ──
   concept            canonical (used here)              legacy alias handled
   hero background     .lesson-hero (solid var(--ink))    (was radial-gradient)
   hero decoration     .lesson-hero::before/::after       (was .lesson-hero-orb*)
   hero badge          .lesson-type-badge                 .lesson-badge(+dot/text)
   hero meta           .lesson-hero-meta(-item)           .lesson-meta(-item)
   content wrapper     .lesson-article > .lesson-article-inner
                                                          .lesson-content (aliased
                                                          below; see NOTE)
   callout             .callout-box(+ -label)             .callout / .callout-title
   nav                 .lesson-nav > .lesson-nav-inner   flat .lesson-nav +
                       (grid, m1-l1 canonical)           .lesson-nav-btn(.overview)
                                                          — BOTH rendered (NOTE 3)
   ═══════════════════════════════════════════════════════════════════════════ */

/* ── Lesson Hero (solid ink) ────────────────────────────────────────────── */
.lesson-hero {
  padding: 6.5rem 2rem 2.5rem;
  background: var(--ink);
  color: #fff;
  position: relative;
  overflow: hidden;
}
.lesson-hero::before {
  content: '';
  position: absolute;
  top: -80px;
  inset-inline-end: -80px;
  width: 320px;
  height: 320px;
  background: rgba(255,255,255,0.03);
  border-radius: 50%;
}
.lesson-hero::after {
  content: '';
  position: absolute;
  bottom: -60px;
  inset-inline-start: -60px;
  width: 240px;
  height: 240px;
  background: rgba(232,168,56,0.06);
  border-radius: 50%;
}
.lesson-hero-inner {
  max-width: 1120px;
  margin-inline: auto;
  position: relative;
  z-index: 1;
}
/* Legacy heroes wrap content in `.container .lesson-hero-content`; keep it
   above the pseudo-orbs. */
.lesson-hero .container { position: relative; z-index: 1; }
.lesson-hero-content { max-width: 720px; position: relative; z-index: 1; }

.lesson-type-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  font-weight: 500;
  padding: 0.3rem 0.85rem;
  border-radius: 100px;
  background: rgba(232,168,56,0.15);
  color: var(--amber);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 1rem;
}
.lesson-type-badge svg { width: 14px; height: 14px; stroke: var(--amber); fill: none; }

.lesson-hero h1 {
  font-family: var(--font-display);
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  font-weight: 700;
  line-height: 1.15;
  margin-bottom: 1rem;
  letter-spacing: -0.02em;
}
.lesson-hero h1 em { font-style: italic; color: var(--amber); }

.lesson-hero-meta { display: flex; align-items: center; gap: 1.5rem; flex-wrap: wrap; }
.lesson-hero-meta-item {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.85rem;
  color: rgba(255,255,255,0.55);
}
.lesson-hero-meta-item svg { width: 16px; height: 16px; stroke: var(--amber); fill: none; }

/* Legacy text-only breadcrumb alias (ml101/la101 Gen-B vocabulary). theme.css
   owns `.lesson-hero .breadcrumb` (the flex/mono form); this is the separate,
   identical-across-both-courses `.lesson-breadcrumb` variant that sits in the
   ink hero and inherits its white text. Aliased here so the 48 inline copies
   are dropped. Token-only. */
.lesson-breadcrumb { font-size: 0.78rem; opacity: 0.5; margin-bottom: 1.25rem; letter-spacing: 0.04em; }
.lesson-breadcrumb a { color: inherit; text-decoration: none; }
.lesson-breadcrumb a:hover { opacity: 1; color: var(--amber); }

/* ── Article body ───────────────────────────────────────────────────────── */
/* `.lesson-content` is the retained legacy single-wrapper alias (NOTE 1). It is
   styled identically to `.lesson-article-inner` so no per-article structural
   markup surgery is needed to migrate. */
.lesson-article { padding: 4rem 2rem 3rem; background: var(--cream); }
.lesson-article-inner,
.lesson-content { max-width: 720px; margin-inline: auto; }
.lesson-content { padding: 3rem 1.5rem 5rem; }

.lesson-article h2,
.lesson-content h2 {
  font-family: var(--font-display);
  font-size: clamp(1.35rem, 3vw, 1.75rem);
  font-weight: 700;
  color: var(--ink);
  margin-block: 3rem 1rem;
  letter-spacing: -0.01em;
  line-height: 1.2;
}
.lesson-article h2:first-child,
.lesson-content h2:first-child { margin-top: 0; }
.lesson-article h3,
.lesson-content h3 {
  font-family: var(--font-display);
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--ink);
  margin-block: 2rem 0.75rem;
  line-height: 1.3;
}
.lesson-article p,
.lesson-content p {
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.8;
  color: var(--text);
  margin-bottom: 1.25rem;
}
.lesson-article ul, .lesson-article ol,
.lesson-content ul, .lesson-content ol {
  padding-inline-start: 1.5rem;
  margin-bottom: 1.25rem;
}
.lesson-article li,
.lesson-content li { font-size: 1rem; line-height: 1.8; color: var(--text); margin-bottom: 0.25rem; }
.lesson-article strong,
.lesson-content strong { color: var(--ink); font-weight: 600; }

/* ── Callout box ────────────────────────────────────────────────────────── */
.callout-box {
  background: var(--white);
  border: 1px solid var(--border-light);
  border-inline-start: 3px solid var(--amber);
  border-radius: var(--r-md);
  padding: 1.5rem 1.75rem;
  margin: 2rem 0;
  box-shadow: var(--shadow-xs);
}
.callout-box-label,
.callout-title {
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--amber);
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.callout-box-label svg { width: 14px; height: 14px; stroke: var(--amber); fill: none; }
.callout-box p { font-size: 0.95rem; line-height: 1.75; margin-bottom: 0.5rem; color: var(--text); }
.callout-box p:last-child { margin-bottom: 0; }
.callout-box strong { color: var(--ink); }
.callout-box .callout-highlight {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  background: var(--amber-pale);
  color: var(--ink);
  padding: 0.75rem 1rem;
  border-radius: var(--r-sm);
  display: block;
  margin-top: 0.75rem;
  line-height: 1.6;
  text-align: center;
}

/* ── Timeline ───────────────────────────────────────────────────────────── */
.timeline {
  background: var(--white);
  border: 1px solid var(--border-light);
  border-radius: var(--r-md);
  padding: 2rem 1.75rem;
  margin: 2rem 0;
  box-shadow: var(--shadow-xs);
}
.timeline-label {
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--amber);
  margin-bottom: 1.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.timeline-label svg { width: 14px; height: 14px; stroke: var(--amber); fill: none; }
.timeline-track { position: relative; padding-inline-start: 2rem; }
.timeline-track::before {
  content: '';
  position: absolute;
  inset-inline-start: 7px;
  top: 4px;
  bottom: 4px;
  width: 2px;
  background: var(--border);
}
.timeline-item { position: relative; padding-bottom: 1.5rem; }
.timeline-item:last-child { padding-bottom: 0; }
.timeline-item::before {
  content: '';
  position: absolute;
  inset-inline-start: -2rem;
  top: 6px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--cream);
  border: 2.5px solid var(--amber);
  z-index: 1;
}
.timeline-item.highlight::before {
  background: var(--amber);
  border-color: var(--amber);
  box-shadow: 0 0 0 4px var(--amber-pale);
}
.timeline-year { font-family: var(--font-mono); font-size: 0.75rem; font-weight: 600; color: var(--ink); margin-bottom: 0.2rem; }
.timeline-desc { font-size: 0.85rem; color: var(--text-secondary); line-height: 1.5; }

/* ── Equation block ─────────────────────────────────────────────────────── */
.equation-block {
  margin: 1.75rem 0;
  padding: 1.5rem 1.25rem;
  border-radius: 16px;
  background: linear-gradient(135deg, var(--surface) 0%, var(--paper) 100%);
  border: 1px solid rgba(0,0,0,0.06);
  position: relative;
  overflow: hidden;
}
.equation-block::before {
  content: '';
  position: absolute;
  top: 0;
  inset-inline-start: 0;
  width: 3px;
  height: 100%;
  background: var(--amber);
}
.equation-block-label {
  font-family: var(--font-mono);
  font-size: 0.6rem;
  font-weight: 700;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--amber);
  margin-bottom: 0.85rem;
  display: flex;
  align-items: center;
  gap: 6px;
}
.equation-block-label svg { width: 13px; height: 13px; stroke: var(--amber); fill: none; stroke-width: 2; stroke-linecap: round; }
/* KaTeX lays out in document order; force LTR so Arabic pages do not reverse it. */
.equation-block .equation-render,
.equation-render { text-align: center; margin: 0.5rem 0; direction: ltr; }
.equation-block .katex-display { margin: 0; }
.equation-block .katex { font-size: 1.2em; color: var(--text); }
.equation-block-caption {
  font-family: var(--font-body);
  font-size: 0.78rem;
  color: rgba(0,0,0,0.5);
  margin-top: 0.75rem;
  line-height: 1.5;
  font-style: italic;
}
.equation-pair { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem; margin: 1.75rem 0; }
.equation-pair .equation-block { margin: 0; }

/* ── Key takeaways (ink card) ───────────────────────────────────────────── */
.takeaways {
  background: var(--ink);
  border-radius: var(--r-lg);
  padding: 2rem 2.25rem;
  margin: 3rem 0 0;
  color: #fff;
}
.takeaways-label,
.takeaways h3 {
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--amber);
  margin: 0 0 1.25rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.takeaways-label svg { width: 14px; height: 14px; stroke: var(--amber); fill: none; }
.takeaways ul { list-style: none; display: flex; flex-direction: column; gap: 0.85rem; padding: 0; margin: 0; }
.takeaways li {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  font-size: 0.95rem;
  line-height: 1.65;
  color: var(--text-on-dark);
}
.takeaways li::before {
  content: '';
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--amber);
  flex-shrink: 0;
  margin-top: 0.5rem;
}

/* ── Lesson nav ─────────────────────────────────────────────────────────── */
/* Two markup shapes are supported from one stylesheet (NOTE 3):
   - GRID (canonical, the m1-l1 reference): `.lesson-nav > .lesson-nav-inner`
     with prev/overview/next + label/title. Selected by :has().
   - FLAT (interim legacy, 41/44 wrl101 files): `.lesson-nav` as a direct flex
     row of `.lesson-nav-btn`(.overview). This is the default below. */
.lesson-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 2rem 0;
  margin-top: 3rem;
  border-top: 1px solid var(--border);
}
.lesson-nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-family: var(--font-body);
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--ink);
  text-decoration: none;
  padding: 0.6rem 1rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  transition: all 0.2s cubic-bezier(0.4,0,0.2,1);
}
.lesson-nav-btn svg { width: 16px; height: 16px; stroke: currentColor; fill: none; stroke-width: 2; flex-shrink: 0; }
.lesson-nav-btn:hover { background: var(--ink); color: var(--cream); border-color: var(--ink); }
.lesson-nav-btn.overview { background: var(--amber); border-color: var(--amber); color: var(--ink); }
.lesson-nav-btn.overview:hover { background: var(--amber-hot); border-color: var(--amber-hot); }

/* GRID form (canonical). When `.lesson-nav` wraps a `.lesson-nav-inner`, drop
   the flat flex on the wrapper and lay the inner out as a 3-column grid. */
.lesson-nav:has(.lesson-nav-inner) {
  display: block;
  padding: 0 2rem;
  margin-top: 0;
  border-top: none;
}
.lesson-nav-inner {
  max-width: 720px;
  margin-inline: auto;
  padding: 2.5rem 0 4rem;
  border-top: 1px solid var(--border);
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 1rem;
  align-items: center;
}
.lesson-nav-inner .lesson-nav-btn {
  padding: 0.7rem 1.25rem;
  border-radius: 100px;
}
.lesson-nav-prev {
  color: var(--text-tertiary);
  border: 1.5px solid var(--border-light);
  cursor: default;
  opacity: 0.5;
  justify-self: start;
}
.lesson-nav-prev svg, .lesson-nav-next svg { width: 16px; height: 16px; fill: none; }
.lesson-nav-prev svg { stroke: var(--text-tertiary); }
.lesson-nav-overview {
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 0.8rem;
  font-weight: 500;
  font-family: var(--font-mono);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  transition: color 0.2s;
  justify-self: center;
}
.lesson-nav-overview:hover { color: var(--ink); }
.lesson-nav-next {
  color: var(--cream);
  background: var(--ink);
  border: 1.5px solid var(--ink);
  justify-self: end;
}
.lesson-nav-next svg { stroke: var(--cream); }
.lesson-nav-next:hover { background: var(--ink-light); transform: translateY(-1px); box-shadow: 0 4px 12px rgba(15,27,45,0.15); }
.lesson-nav-label {
  font-family: var(--font-mono);
  font-size: 0.6rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  opacity: 0.6;
  display: block;
  margin-bottom: 0.1rem;
}
.lesson-nav-title { display: block; line-height: 1.3; }

/* ── Tables (shared) ────────────────────────────────────────────────────── */
.table-scroll { overflow-x: auto; }
.data-table { width: 100%; border-collapse: collapse; margin: 1.5rem 0; font-size: 0.82rem; }
.data-table th, .data-table td { border: 1px solid rgba(0,0,0,0.1); padding: 0.6rem 0.7rem; text-align: start; line-height: 1.4; }
.data-table th {
  background: var(--ink);
  color: var(--cream);
  font-family: var(--font-mono);
  font-size: 0.68rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  font-weight: 600;
}
.data-table td { color: var(--text-secondary); vertical-align: top; }
.data-table code { font-family: var(--font-mono); font-size: 0.9em; color: var(--ink); }
.data-table tr:nth-child(even) td { background: var(--surface); }
.example-table { width: 100%; border-collapse: collapse; margin: 1.5rem 0; font-size: 0.88rem; }
.example-table th {
  background: var(--ink);
  color: var(--amber);
  padding: 0.6rem 1rem;
  text-align: start;
  font-weight: 600;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  letter-spacing: 0.05em;
}
.example-table td { padding: 0.6rem 1rem; border-bottom: 1px solid rgba(0,0,0,0.06); color: var(--text); }
.example-table tr:last-child td { border-bottom: none; }
.example-table tr:nth-child(even) td { background: rgba(0,0,0,0.02); }

/* ── Misc shared ────────────────────────────────────────────────────────── */
.teaser {
  background: var(--surface);
  border: 1px solid var(--border-light);
  border-radius: var(--r-md);
  padding: 1.25rem 1.5rem;
  margin-top: 1rem;
}
.teaser p { font-style: italic; color: var(--text-secondary); margin-bottom: 0; font-size: 0.95rem; }
.divider { border: none; border-top: 1px solid rgba(0,0,0,0.07); margin: 3rem 0; }

.lang-switch { display: flex; align-items: center; gap: 0.25rem; }
.lang-switch a {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-tertiary);
  text-decoration: none;
  padding: 0.3rem 0.6rem;
  border-radius: 6px;
  transition: all 0.2s;
}
.lang-switch a:hover { color: var(--ink); }
.lang-switch a.active { background: var(--amber-pale); color: var(--amber); }
.lang-switch a::after { display: none !important; }

/* ── Responsive ─────────────────────────────────────────────────────────── */
@media (max-width: 768px) {
  .lesson-hero { padding: 5.5rem 1.5rem 2rem; }
  .lesson-article { padding: 3rem 1.5rem 2rem; }
  .lesson-content { padding: 2.5rem 1.25rem 4rem; }
}
@media (max-width: 600px) {
  .equation-pair { grid-template-columns: 1fr; }
  .equation-block .katex { font-size: 1em; }
}
@media (max-width: 480px) {
  .lesson-hero h1 { font-size: 1.5rem; }
  .lesson-hero-meta { gap: 0.75rem; }
  .lesson-nav { flex-wrap: wrap; }
}