/* ── Variables ─────────────────────────────────────────── */
:root {
  --navy:       #0f172a;
  --navy-mid:   #1e293b;
  --navy-light: #334155;
  --teal:       #0ea5e9;
  --teal-dark:  #0284c7;
  --teal-pale:  #e0f2fe;
  --white:      #ffffff;
  --grey-50:    #f8fafc;
  --grey-100:   #f1f5f9;
  --grey-200:   #e2e8f0;
  --grey-400:   #94a3b8;
  --grey-600:   #475569;
  --grey-700:   #334155;
  --grey-800:   #1e293b;
  --green:      #10b981;
  --green-pale: #d1fae5;
  --green-dark: #065f46;
  --amber:      #f59e0b;
  --amber-pale: #fef3c7;
  --amber-dark: #92400e;
  --purple:     #8b5cf6;
  --purple-pale:#ede9fe;
  --purple-dark:#4c1d95;
  --radius:     10px;
  --shadow-sm:  0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.05);
  --shadow:     0 4px 6px -1px rgba(0,0,0,.08), 0 2px 4px -2px rgba(0,0,0,.06);
  --shadow-md:  0 10px 15px -3px rgba(0,0,0,.08), 0 4px 6px -4px rgba(0,0,0,.05);
  --nav-h:      60px;
  --t:          .18s ease;
  --content-w:  860px;
}

/* ── Reset ─────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: system-ui, -apple-system, 'Segoe UI', Roboto, sans-serif;
  background: var(--grey-50);
  color: var(--grey-800);
  line-height: 1.65;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
#app { flex: 1; }
a { color: var(--teal); text-decoration: none; transition: color var(--t); }
a:hover { color: var(--teal-dark); }
ul, ol { list-style: none; }
img { max-width: 100%; display: block; }

/* ── Navbar ────────────────────────────────────────────── */
.navbar {
  background: var(--navy);
  position: sticky;
  top: 0;
  z-index: 200;
  height: var(--nav-h);
  box-shadow: 0 2px 12px rgba(0,0,0,.3);
}
.nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1.5rem;
  height: 100%;
  display: flex;
  align-items: center;
}
.nav-brand {
  color: var(--white);
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -.01em;
  display: flex;
  align-items: center;
  gap: .5rem;
  white-space: nowrap;
  text-decoration: none;
  margin-right: auto;
}
.brand-mono {
  color: var(--teal);
  font-family: monospace;
  font-weight: 800;
  font-size: 1rem;
}
.nav-links {
  display: flex;
  align-items: center;
  gap: .2rem;
}
.nav-links li a {
  color: rgba(255,255,255,.7);
  font-size: .875rem;
  font-weight: 500;
  padding: .4rem .9rem;
  border-radius: 7px;
  transition: color var(--t), background var(--t);
  display: block;
}
.nav-links li a:hover { color: var(--white); background: rgba(255,255,255,.08); }
.nav-links li a.active { color: var(--white); background: rgba(14,165,233,.22); }
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 6px;
  margin-left: 1rem;
}
.nav-toggle span {
  display: block;
  width: 22px; height: 2px;
  background: var(--white);
  border-radius: 2px;
  transition: transform var(--t), opacity var(--t);
}
.nav-toggle.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle.open span:nth-child(2) { opacity: 0; }
.nav-toggle.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ── Breadcrumb ────────────────────────────────────────── */
.breadcrumb {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: .35rem;
  font-size: .78rem;
  color: rgba(255,255,255,.45);
  margin-bottom: .9rem;
}
.breadcrumb a { color: rgba(255,255,255,.6); }
.breadcrumb a:hover { color: var(--teal); }
.bc-sep { color: rgba(255,255,255,.25); }

/* ── Hero / Topic Header ───────────────────────────────── */
.page-hero {
  background: linear-gradient(135deg, var(--navy) 0%, var(--navy-mid) 55%, #164e63 100%);
  padding: 4rem 1.5rem 3.5rem;
  color: var(--white);
  text-align: center;
}
.hero-eyebrow {
  display: inline-block;
  background: rgba(14,165,233,.15);
  color: var(--teal);
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .12em;
  text-transform: uppercase;
  padding: .3rem 1rem;
  border-radius: 999px;
  border: 1px solid rgba(14,165,233,.28);
  margin-bottom: 1.25rem;
}
.page-hero h1 {
  font-size: clamp(1.9rem,4.5vw,3rem);
  font-weight: 800;
  letter-spacing: -.03em;
  line-height: 1.15;
  margin-bottom: 1rem;
}
.page-hero h1 span { color: var(--teal); }
.page-hero .hero-sub {
  font-size: 1.05rem;
  color: rgba(255,255,255,.65);
  max-width: 520px;
  margin: 0 auto 2.5rem;
}
.topic-hero {
  background: var(--navy);
  padding: 2.25rem 1.5rem 2rem;
  color: var(--white);
}
.topic-hero-inner { max-width: 1100px; margin: 0 auto; }
.topic-code-pill {
  display: inline-block;
  background: var(--teal);
  color: var(--white);
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .06em;
  text-transform: uppercase;
  padding: .22rem .7rem;
  border-radius: 5px;
  margin-bottom: .75rem;
}
.topic-hero h1 {
  font-size: clamp(1.4rem,3vw,2rem);
  font-weight: 800;
  letter-spacing: -.025em;
  margin-bottom: .45rem;
}
.topic-hero .topic-sub { color: rgba(255,255,255,.6); font-size: .9rem; max-width: 640px; }

/* ── Lesson Hero ───────────────────────────────────────── */
.lesson-hero {
  background: linear-gradient(to right, var(--navy) 0%, var(--navy-mid) 100%);
  padding: 2.5rem 1.5rem 2.25rem;
  color: var(--white);
  border-bottom: 1px solid rgba(14,165,233,.2);
}
.lesson-hero-inner { max-width: var(--content-w); margin: 0 auto; }
.lesson-meta {
  display: flex;
  align-items: center;
  gap: .75rem;
  margin-bottom: .75rem;
  flex-wrap: wrap;
}
.lesson-num {
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--teal);
  background: rgba(14,165,233,.15);
  border: 1px solid rgba(14,165,233,.3);
  padding: .22rem .7rem;
  border-radius: 5px;
}
.lesson-ref {
  font-size: .72rem;
  color: rgba(255,255,255,.45);
  font-family: monospace;
}
.lesson-hero h1 {
  font-size: clamp(1.35rem,2.5vw,1.9rem);
  font-weight: 800;
  letter-spacing: -.025em;
  margin-bottom: .75rem;
  line-height: 1.25;
}
.lesson-objectives {
  background: rgba(255,255,255,.06);
  border-left: 3px solid var(--teal);
  border-radius: 0 8px 8px 0;
  padding: .85rem 1rem;
  font-size: .875rem;
  color: rgba(255,255,255,.75);
  line-height: 1.6;
}
.lesson-objectives strong { color: var(--teal); }

/* ── Page / Content Layout ─────────────────────────────── */
.page-section {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2.5rem 1.5rem;
}
.lesson-body {
  max-width: var(--content-w);
  margin: 0 auto;
  padding: 2.5rem 1.5rem 3rem;
}
.lesson-section { margin-bottom: 2.5rem; }
.lesson-section h2 {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--navy);
  letter-spacing: -.02em;
  margin-bottom: 1rem;
  padding-bottom: .5rem;
  border-bottom: 2px solid var(--grey-200);
}
.lesson-section h3 {
  font-size: 1rem;
  font-weight: 700;
  color: var(--grey-700);
  margin: 1.25rem 0 .5rem;
}
.lesson-section p { color: var(--grey-700); font-size: .9375rem; margin-bottom: .75rem; }
.lesson-section p:last-child { margin-bottom: 0; }

/* ── Home Cards ────────────────────────────────────────── */
.home-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px,1fr));
  gap: 1.5rem;
  max-width: 1100px;
  margin: 0 auto;
}
.home-card {
  background: rgba(255,255,255,.07);
  border: 1px solid rgba(255,255,255,.12);
  border-radius: 14px;
  padding: 2rem 1.75rem;
  display: flex;
  flex-direction: column;
  gap: .7rem;
  text-decoration: none;
  transition: background var(--t), border-color var(--t), transform var(--t);
}
.home-card:hover {
  background: rgba(255,255,255,.11);
  border-color: var(--teal);
  transform: translateY(-3px);
}
.home-card-icon { font-size: 2rem; line-height: 1; }
.home-card-label {
  font-size: .68rem;
  font-weight: 700;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--teal);
}
.home-card h3 {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--white);
  letter-spacing: -.02em;
  line-height: 1.2;
}
.home-card p {
  font-size: .85rem;
  color: rgba(255,255,255,.58);
  line-height: 1.55;
  flex: 1;
}
.home-card-arrow { color: var(--teal); font-size: .875rem; margin-top: .25rem; }

/* ── Topic Cards ───────────────────────────────────────── */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(268px,1fr));
  gap: 1.1rem;
}
.card {
  background: var(--white);
  border: 1px solid var(--grey-200);
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  display: flex;
  flex-direction: column;
  transition: box-shadow var(--t), transform var(--t), border-color var(--t);
}
.card:hover { box-shadow: var(--shadow-md); transform: translateY(-2px); border-color: #cbd5e1; }
a.card, .card-link {
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
  height: 100%;
}
.card-top {
  padding: 1.1rem 1.2rem .6rem;
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: .6rem;
}
.card-code {
  font-size: .7rem;
  font-weight: 700;
  letter-spacing: .05em;
  color: var(--teal);
  background: var(--teal-pale);
  padding: .18rem .55rem;
  border-radius: 5px;
  flex-shrink: 0;
}
.card-body-area {
  padding: .35rem 1.2rem 1.1rem;
  flex: 1;
  display: flex;
  flex-direction: column;
}
.card-title {
  font-size: .9375rem;
  font-weight: 600;
  color: var(--grey-800);
  margin-bottom: .3rem;
  line-height: 1.35;
}
.card-desc {
  font-size: .825rem;
  color: var(--grey-600);
  flex: 1;
  line-height: 1.5;
}
.card-foot {
  padding: .65rem 1.2rem;
  border-top: 1px solid var(--grey-100);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: .5rem;
}
.card-arrow { color: var(--teal); font-size: .8rem; font-weight: 600; }

/* ── Lesson Cards (A3 list) ────────────────────────────── */
.lesson-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px,1fr));
  gap: 1rem;
  margin-top: 1.5rem;
}
.lesson-card {
  background: var(--white);
  border: 1px solid var(--grey-200);
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: inherit;
  transition: box-shadow var(--t), transform var(--t), border-color var(--t);
}
.lesson-card:hover { box-shadow: var(--shadow-md); transform: translateY(-2px); border-color: var(--teal); }
.lesson-card-top {
  background: var(--navy);
  padding: .85rem 1rem .75rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.lesson-card-num {
  font-size: .7rem;
  font-weight: 700;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--teal);
}
.lesson-card-body { padding: .85rem 1rem 1rem; flex: 1; }
.lesson-card-title {
  font-size: .9375rem;
  font-weight: 600;
  color: var(--grey-800);
  margin-bottom: .35rem;
  line-height: 1.35;
}
.lesson-card-ref {
  font-size: .75rem;
  color: var(--grey-400);
  font-family: monospace;
}
.lesson-card-foot {
  padding: .6rem 1rem;
  border-top: 1px solid var(--grey-100);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* ── Badges ────────────────────────────────────────────── */
.badge-group { display: flex; flex-wrap: wrap; gap: .3rem; }
.badge {
  display: inline-flex;
  align-items: center;
  font-size: .67rem;
  font-weight: 700;
  letter-spacing: .04em;
  padding: .18rem .5rem;
  border-radius: 999px;
}
.badge-sl  { background: var(--green-pale);  color: var(--green-dark); }
.badge-hl  { background: var(--amber-pale);  color: var(--amber-dark); }
.badge-hlo { background: var(--purple-pale); color: var(--purple-dark); }

/* ── Paper divider ─────────────────────────────────────── */
.paper-divider {
  margin: 2.25rem 0 1.1rem;
  display: flex;
  align-items: center;
  gap: .9rem;
}
.paper-divider h3 {
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--grey-600);
  white-space: nowrap;
}
.paper-line { flex: 1; height: 1px; background: var(--grey-200); }

/* ── Coming soon ───────────────────────────────────────── */
.coming-soon {
  font-size: .72rem;
  color: var(--grey-400);
  display: flex;
  align-items: center;
  gap: .3rem;
}
.coming-soon::before {
  content: '';
  display: inline-block;
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--grey-200);
}

/* ── Definition boxes ──────────────────────────────────── */
.def-box {
  border-left: 4px solid var(--teal);
  background: var(--teal-pale);
  padding: .9rem 1.1rem;
  border-radius: 0 8px 8px 0;
  margin: .85rem 0;
}
.def-box .def-term {
  font-weight: 700;
  font-size: .875rem;
  color: var(--navy);
  margin-bottom: .25rem;
}
.def-box p { color: var(--grey-700); font-size: .875rem; margin: 0; }

/* ── Callout boxes ─────────────────────────────────────── */
.callout {
  padding: .9rem 1.1rem;
  border-radius: 0 8px 8px 0;
  margin: 1rem 0;
}
.callout-label {
  font-size: .68rem;
  font-weight: 700;
  letter-spacing: .08em;
  text-transform: uppercase;
  margin-bottom: .3rem;
}
.callout p { font-size: .875rem; margin: 0; }
.callout-exam  { border-left: 4px solid var(--amber); background: var(--amber-pale); }
.callout-exam  .callout-label { color: var(--amber-dark); }
.callout-exam  p { color: #713f12; }
.callout-tip   { border-left: 4px solid var(--green); background: var(--green-pale); }
.callout-tip   .callout-label { color: var(--green-dark); }
.callout-tip   p { color: #064e3b; }
.callout-hl    { border-left: 4px solid var(--purple); background: var(--purple-pale); }
.callout-hl    .callout-label { color: var(--purple-dark); }
.callout-hl    p { color: var(--purple-dark); }

/* ── Key terms grid ────────────────────────────────────── */
.key-terms-box {
  background: var(--grey-100);
  border: 1px solid var(--grey-200);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
}
.key-terms-box h3 {
  font-size: .75rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--grey-600);
  margin-bottom: 1rem;
  border-bottom: none;
  padding-bottom: 0;
}
.key-terms-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px,1fr));
  gap: .6rem;
}
.key-term {
  background: var(--white);
  border: 1px solid var(--grey-200);
  border-radius: 7px;
  padding: .6rem .85rem;
}
.kt-name {
  display: block;
  font-size: .8rem;
  font-weight: 700;
  color: var(--teal-dark);
  margin-bottom: .2rem;
}
.kt-def { font-size: .8rem; color: var(--grey-600); line-height: 1.45; }

/* ── Content table ─────────────────────────────────────── */
.tbl-wrap { overflow-x: auto; margin: 1rem 0; }
.content-table {
  width: 100%;
  border-collapse: collapse;
  font-size: .85rem;
  min-width: 480px;
}
.content-table th {
  background: var(--navy-mid);
  color: var(--white);
  padding: .65rem 1rem;
  text-align: left;
  font-size: .75rem;
  letter-spacing: .05em;
  text-transform: uppercase;
  font-weight: 700;
}
.content-table td {
  padding: .6rem 1rem;
  border-bottom: 1px solid var(--grey-100);
  color: var(--grey-700);
  vertical-align: top;
  line-height: 1.5;
}
.content-table tr:last-child td { border-bottom: none; }
.content-table tr:nth-child(even) td { background: var(--grey-50); }
.content-table code {
  background: var(--grey-100);
  padding: .1rem .35rem;
  border-radius: 4px;
  font-family: 'Cascadia Code', Consolas, monospace;
  font-size: .85em;
  color: var(--teal-dark);
}
.content-table .tag-hl {
  font-size: .65rem;
  font-weight: 700;
  background: var(--purple-pale);
  color: var(--purple-dark);
  padding: .1rem .45rem;
  border-radius: 999px;
}

/* ── Code blocks ───────────────────────────────────────── */
.code-block {
  background: #0d1117;
  color: #c9d1d9;
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  font-family: 'Cascadia Code', 'Fira Code', Consolas, monospace;
  font-size: .845rem;
  line-height: 1.65;
  overflow-x: auto;
  margin: 1rem 0;
  border: 1px solid #21262d;
  white-space: pre;
}
.code-block .kw  { color: #79c0ff; font-weight: 600; }
.code-block .str { color: #a5d6ff; }
.code-block .num { color: #ffa657; }
.code-block .cmt { color: #6e7681; font-style: italic; }
.code-block .fn  { color: #d2a8ff; }

/* ── Two-column feature list ───────────────────────────── */
.two-col-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px,1fr));
  gap: .6rem;
  margin: .75rem 0;
}
.list-item {
  background: var(--white);
  border: 1px solid var(--grey-200);
  border-radius: 8px;
  padding: .75rem 1rem;
  font-size: .875rem;
  color: var(--grey-700);
  line-height: 1.5;
  display: flex;
  gap: .6rem;
  align-items: flex-start;
}
.list-item .li-icon {
  flex-shrink: 0;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: .7rem;
  font-weight: 800;
  margin-top: .1rem;
}
.li-benefit .li-icon { background: var(--green-pale); color: var(--green-dark); }
.li-limit   .li-icon { background: #fee2e2; color: #991b1b; }
.li-neutral .li-icon { background: var(--teal-pale); color: var(--teal-dark); }
.list-item strong { color: var(--grey-800); font-weight: 600; }

/* ── Back link ─────────────────────────────────────────── */
.back-link {
  display: inline-flex;
  align-items: center;
  gap: .4rem;
  font-size: .825rem;
  color: var(--grey-600);
  margin-bottom: 2rem;
  transition: color var(--t);
}
.back-link:hover { color: var(--teal); }

/* ── Lesson prev/next nav ──────────────────────────────── */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: stretch;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 2px solid var(--grey-200);
}
.lesson-nav-btn {
  display: flex;
  flex-direction: column;
  gap: .2rem;
  padding: .9rem 1.2rem;
  border: 1.5px solid var(--grey-200);
  border-radius: var(--radius);
  text-decoration: none;
  color: var(--grey-700);
  background: var(--grey-50);
  transition: border-color var(--t), background var(--t), color var(--t);
  min-width: 0;
  max-width: 48%;
}
.lesson-nav-btn:hover {
  border-color: var(--teal);
  background: var(--white);
  color: var(--teal);
}
.lesson-nav-btn.next { text-align: right; margin-left: auto; }
.lesson-nav-label {
  font-size: .7rem;
  font-weight: 600;
  letter-spacing: .06em;
  text-transform: uppercase;
  color: var(--grey-400);
}
.lesson-nav-btn:hover .lesson-nav-label { color: var(--teal); opacity: .7; }
.lesson-nav-title { font-size: .9rem; font-weight: 600; }

/* ── Section header ────────────────────────────────────── */
.section-header { margin-bottom: 1.5rem; }
.section-header h2 {
  font-size: 1.4rem;
  font-weight: 700;
  color: var(--grey-800);
  letter-spacing: -.02em;
  margin-bottom: .3rem;
}
.section-header p { color: var(--grey-600); font-size: .9rem; }

/* ── Overview intro box ────────────────────────────────── */
.overview-box {
  background: var(--white);
  border: 1px solid var(--grey-200);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin-bottom: 2rem;
  color: var(--grey-600);
  font-size: .9375rem;
  line-height: 1.7;
}

/* ── IB DP overview SL/HL cards ───────────────────────── */
.overview-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1.25rem;
  margin-bottom: 1rem;
}
.overview-card {
  background: var(--white);
  border: 1px solid var(--grey-200);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
}
.ov-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--navy);
  margin-bottom: .25rem;
}
.ov-hours {
  font-size: .82rem;
  color: var(--teal);
  font-weight: 600;
  margin-bottom: .75rem;
}
.ov-list {
  margin: 0;
  padding-left: 1.25rem;
  color: var(--grey-600);
  font-size: .875rem;
  line-height: 1.8;
}

/* ── Footer ────────────────────────────────────────────── */
.footer { background: var(--navy); padding: 1.25rem 1.5rem; }
.footer-inner { max-width: 1100px; margin: 0 auto; text-align: center; }
.footer p { color: rgba(255,255,255,.35); font-size: .78rem; }

/* ── Responsive ────────────────────────────────────────── */
@media (max-width: 700px) {
  .nav-toggle { display: flex; }
  .nav-links {
    display: none;
    position: fixed;
    top: var(--nav-h);
    left: 0; right: 0;
    background: var(--navy-mid);
    flex-direction: column;
    align-items: stretch;
    padding: .75rem;
    gap: .2rem;
    border-bottom: 1px solid rgba(255,255,255,.07);
    box-shadow: 0 8px 24px rgba(0,0,0,.4);
    z-index: 199;
  }
  .nav-links.open { display: flex; }
  .nav-links li a { padding: .75rem 1rem; }
  .card-grid, .lesson-grid { grid-template-columns: 1fr; }
  .home-cards { grid-template-columns: 1fr; }
  .page-hero { padding: 3rem 1.25rem 2.5rem; }
  .lesson-body, .page-section { padding-left: 1.1rem; padding-right: 1.1rem; }
  .key-terms-grid { grid-template-columns: 1fr; }
  .two-col-list { grid-template-columns: 1fr; }
}
@media (max-width: 480px) {
  .code-block { font-size: .78rem; padding: 1rem 1rem; }
}

/* ── Practice Q&A accordion ───────────────────────── */
.qa-block { margin: 2rem 0; }
.qa-block h3 { font-size: 1.05rem; font-weight: 700; color: var(--teal); margin-bottom: .75rem; }
.qa-item {
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: .5rem;
  overflow: hidden;
  background: var(--card-bg);
}
.qa-item[open] { border-color: var(--teal); }
.qa-question {
  cursor: pointer;
  padding: .85rem 1rem;
  font-weight: 600;
  font-size: .95rem;
  color: var(--text);
  list-style: none;
  display: flex;
  align-items: center;
  gap: .6rem;
  user-select: none;
}
.qa-question::before {
  content: '▶';
  font-size: .6rem;
  color: var(--teal);
  flex-shrink: 0;
  transition: transform .15s;
}
.qa-item[open] > .qa-question::before { transform: rotate(90deg); }
.qa-question::-webkit-details-marker { display: none; }
.qa-answer {
  padding: .75rem 1rem 1rem 1rem;
  border-top: 1px solid var(--border);
  font-size: .9rem;
  color: var(--text-muted);
  line-height: 1.6;
}