:root {
  color-scheme: dark;
  font-family: "Inter", "Segoe UI", system-ui, sans-serif;
  background: #101217;
  color: #f1f2f6;
  --muted: #afb6c8;
  --line: #323747;
  --surface: #191d28;
  --accent: #a8f0ce;
  --lavender: #c9bbff;
}
* { box-sizing: border-box; }
body { margin: 0; }
a { color: var(--accent); text-underline-offset: .25em; }
button, textarea { font: inherit; }
button, summary { cursor: pointer; }
:focus-visible { outline: 3px solid var(--lavender); outline-offset: 4px; }
.top { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: .65rem 1rem; padding: .85rem clamp(1rem, 5vw, 4rem); border-bottom: 1px solid var(--line); }
.brand, .top-links, #language { display: flex; align-items: center; gap: .65rem; }
.brand, .external, #language a { text-decoration: none; font-weight: 650; }
.brand { color: inherit; letter-spacing: .06em; }
.brand img { display: block; width: clamp(215px, 27vw, 290px); height: auto; max-width: 70vw; }
.brand small { color: var(--accent); }
#language a { padding: .35rem .5rem; color: var(--muted); border-radius: .4rem; }
#language [aria-current] { color: var(--accent); background: var(--surface); }
.external { padding-left: .8rem; border-left: 1px solid var(--line); }
.shell { max-width: 1320px; margin: auto; display: grid; grid-template-columns: 270px minmax(0, 1fr); min-height: calc(100vh - 65px); }
aside { padding: 2rem 1.15rem; border-right: 1px solid var(--line); }
aside nav a { display: grid; grid-template-columns: 1.5rem 1fr; gap: .55rem; align-items: baseline; text-decoration: none; color: var(--muted); padding: .6rem .65rem; margin: .15rem 0; border-radius: .45rem; font-size: .92rem; }
aside nav a:hover, aside nav a[aria-current] { background: var(--surface); color: var(--accent); }
aside nav span { color: var(--accent); font-family: monospace; }
.progress { display: grid; gap: .55rem; padding: .65rem; color: var(--muted); font-size: .85rem; }
progress { width: 100%; height: .65rem; accent-color: var(--accent); }
main { padding: clamp(1rem, 4vw, 3.2rem); line-height: 1.65; overflow-wrap: anywhere; }
h1, h2, h3 { line-height: 1.12; letter-spacing: -.035em; }
h1 { font-size: clamp(2.15rem, 6vw, 4.55rem); margin: .5rem 0 1rem; max-width: 14ch; }
h2 { font-size: clamp(1.4rem, 3vw, 2rem); margin-top: 0; }
h3 { font-size: 1.2rem; }
p { max-width: 75ch; }
.hero { padding: clamp(1.3rem, 5vw, 3rem); border: 1px solid var(--line); border-radius: 1.2rem; background: radial-gradient(ellipse at top right, #303050, transparent 70%), #171b25; }
.eyebrow { color: var(--accent); font-family: monospace; font-size: .9rem; letter-spacing: .12em; text-transform: uppercase; }
.lead, figcaption, .muted { color: var(--muted); }
.lead { font-size: 1.12rem; }
.workflow { display: grid; grid-template-columns: repeat(4, 1fr); gap: .55rem; margin: 2rem 0 0; padding: 0; list-style: none; }
.workflow a { display: block; height: 100%; padding: .75rem; text-decoration: none; border: 1px solid var(--line); border-radius: .6rem; background: #131722; font-weight: 650; transition: background .2s, transform .2s; }
.workflow a:hover { background: #272d3e; transform: translateY(-3px); }
.workflow small { display: block; color: var(--muted); font-weight: 400; margin-top: .3rem; }
.button { display: inline-block; border: 1px solid var(--accent); border-radius: .5rem; padding: .55rem .9rem; color: #122820; background: var(--accent); text-decoration: none; font-weight: 700; }
.secondary { color: var(--accent); background: transparent; }
.panel { border: 1px solid var(--line); background: var(--surface); border-radius: .85rem; padding: clamp(1rem, 3vw, 1.55rem); margin-top: 1.3rem; }
.lesson { max-width: 78ch; }
.lesson h2 { margin-top: 1.55rem; }
fieldset { border: 0; padding: 0; margin: 0; }
legend { margin-bottom: .65rem; font-weight: 650; }
.choice { display: flex; align-items: baseline; gap: .7rem; padding: .55rem .75rem; margin: .35rem 0; border: 1px solid var(--line); border-radius: .45rem; cursor: pointer; }
.choice:has(:checked) { border-color: var(--lavender); }
.choice input { accent-color: var(--lavender); }
.feedback { min-height: 1.65em; }
.feedback[data-result="correct"] { color: var(--accent); }
.feedback[data-result="retry"] { color: #ffd4a4; }
textarea { display: block; background: #11141c; color: inherit; width: 100%; min-height: 7rem; padding: .8rem; border: 1px solid var(--line); border-radius: .5rem; margin: .45rem 0 .9rem; }
details { margin: 1rem 0 0; }
summary { color: var(--accent); font-weight: 650; }
.document { margin-top: .65rem; padding: 1rem; border: 1px solid var(--line); border-radius: .5rem; background: #11141c; max-height: 31rem; overflow: auto; }
.document p, .document li { max-width: 80ch; }
.document pre { white-space: pre-wrap; }
.document table { border-collapse: collapse; width: 100%; font-size: .9rem; }
.document :is(td, th) { padding: .35rem .55rem; border: 1px solid var(--line); text-align: left; }
figure { margin: 1.4rem 0; }
figure img { display: block; width: min(100%, 640px); border-radius: .6rem; border: 1px solid var(--line); }
.footer-nav { margin-top: 1.8rem; display: flex; flex-wrap: wrap; justify-content: space-between; gap: .8rem; }
.section-list { columns: 2; padding-left: 1.7rem; }
.section-list li { break-inside: avoid; padding: .25rem 0; }
main > * { animation: appear .25s ease-out both; }
@keyframes appear { from { opacity: .5; transform: translateY(5px); } to { opacity: 1; transform: translateY(0); } }
@media (max-width: 780px) {
  .shell { grid-template-columns: minmax(0, 1fr); }
  aside { border-right: 0; border-bottom: 1px solid var(--line); padding: .55rem 1rem; }
  aside details { margin: .35rem 0; }
  .workflow { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 420px) { .section-list { columns: 1; } }
@media (prefers-reduced-motion: reduce) { *, *::before, *::after { animation: none !important; transition: none !important; } }