:root {
  --bg: #090815;
  --panel: #111123;
  --panel-2: #18172d;
  --ink: #f3f4ff;
  --muted: #9ca2ba;
  --cyan: #52e2f2;
  --amber: #ffca61;
  --line: rgba(255, 255, 255, 0.12);
  color-scheme: dark;
  font-family: "Manrope", "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  color: var(--ink);
  background:
    radial-gradient(circle at 75% -10%, rgba(78, 84, 255, 0.25), transparent 34rem),
    linear-gradient(135deg, var(--bg), #0b1020 70%, #111022);
}

a { color: inherit; }

.site-header {
  min-height: 72px;
  padding: 0 5vw;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--line);
  background: rgba(9, 8, 21, 0.78);
  backdrop-filter: blur(18px);
  position: sticky;
  top: 0;
  z-index: 20;
}

.site-header nav { display: flex; align-items: center; gap: 1rem; color: var(--muted); }
.site-header form { margin: 0; }
.brand { font: 800 1rem/1 "JetBrains Mono", monospace; letter-spacing: 0.13em; text-decoration: none; }
.brand span { color: var(--cyan); }
.link-button { padding: 0; color: var(--cyan); background: none; border: 0; font: inherit; cursor: pointer; }

.hero {
  min-height: 55vh;
  padding: clamp(5rem, 12vw, 10rem) 8vw 5rem;
  display: grid;
  align-content: center;
  border-bottom: 1px solid var(--line);
}

.eyebrow { color: var(--cyan); font: 700 0.72rem/1.4 "JetBrains Mono", monospace; letter-spacing: 0.16em; text-transform: uppercase; }
h1 { max-width: 13ch; margin: 0.3rem 0 1rem; font-size: clamp(3rem, 9vw, 8.5rem); line-height: 0.9; letter-spacing: -0.065em; }
.hero-intro, .page-heading > p { max-width: 58rem; color: var(--muted); font-size: clamp(1.05rem, 2vw, 1.35rem); line-height: 1.65; }

.page-grid { display: grid; grid-template-columns: repeat(12, 1fr); gap: 1px; background: var(--line); border-bottom: 1px solid var(--line); }
.page-card, .empty-state { grid-column: span 6; min-height: 280px; padding: clamp(2rem, 5vw, 4.5rem); background: var(--panel); text-decoration: none; transition: background 180ms ease, transform 180ms ease; }
.page-card:hover { position: relative; background: var(--panel-2); transform: translateY(-3px); }
.page-card::before { content: ""; display: block; width: 56px; height: 3px; margin-bottom: 2.5rem; background: var(--accent, var(--amber)); }
.page-card h2, .empty-state h2 { margin: 0 0 1rem; font-size: clamp(1.6rem, 3vw, 2.6rem); }
.page-card p, .empty-state p { max-width: 42rem; color: var(--muted); line-height: 1.65; }
.card-index, .card-meta { font: 600 0.75rem/1.4 "JetBrains Mono", monospace; color: var(--cyan) !important; }

.content-shell, .lesson-shell { width: min(1180px, 90vw); margin: 0 auto; padding: 4rem 0 8rem; }
.lesson-shell { width: min(820px, 90vw); }
.breadcrumb { display: inline-block; margin-bottom: 5rem; color: var(--muted); text-decoration: none; }
.page-heading { padding-bottom: 4rem; border-bottom: 1px solid var(--line); }
.page-heading h1 { font-size: clamp(3rem, 7vw, 6.5rem); }
.content-shell .page-grid { margin-top: 3rem; border: 1px solid var(--line); }

.lesson-list { margin: 3rem 0 0; padding: 0; list-style: none; border-top: 1px solid var(--line); }
.lesson-list a { display: grid; grid-template-columns: 4rem 1fr auto; gap: 1rem; padding: 1.5rem 0; align-items: center; border-bottom: 1px solid var(--line); text-decoration: none; }
.lesson-list span, .lesson-list small { color: var(--muted); font-family: "JetBrains Mono", monospace; }

.lesson-body { padding-top: 3rem; font-size: 1.08rem; line-height: 1.8; }
.lesson-body h2, .lesson-body h3 { margin-top: 3rem; line-height: 1.2; }
.callout { margin: 2rem 0; padding: 1.5rem 1.75rem; border-left: 4px solid var(--cyan); background: rgba(82, 226, 242, 0.07); }
.callout-warning { border-color: var(--amber); background: rgba(255, 202, 97, 0.07); }
.callout-exam { border-color: #ff6d91; background: rgba(255, 109, 145, 0.07); }
.code-block { margin: 2rem 0; border: 1px solid var(--line); background: #060611; }
.code-block figcaption { padding: 0.7rem 1rem; color: var(--cyan); border-bottom: 1px solid var(--line); font: 600 0.75rem "JetBrains Mono", monospace; }
.code-block pre { margin: 0; padding: 1.5rem; overflow-x: auto; }

.physics-catalog {
  --physics-blue: #5de7f2;
  --physics-amber: #ffca61;
  --physics-violet: #9290ff;
  width: min(1320px, calc(100% - 3rem));
  margin: 0 auto;
  padding: 2rem 0 8rem;
}

.physics-hero {
  position: relative;
  min-height: 620px;
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(240px, .65fr);
  align-items: end;
  gap: 4rem;
  overflow: hidden;
  padding: clamp(3rem, 7vw, 7rem);
  border: 1px solid var(--line);
  background:
    linear-gradient(125deg, rgba(8, 10, 27, .96) 0 48%, rgba(18, 23, 54, .7)),
    radial-gradient(circle at 75% 24%, rgba(93, 231, 242, .3), transparent 27rem);
}

.physics-hero::before {
  content: "F = ma";
  position: absolute;
  right: -1rem;
  bottom: -2.8rem;
  color: rgba(255, 255, 255, .035);
  font: 800 clamp(7rem, 18vw, 17rem)/1 "JetBrains Mono", monospace;
  letter-spacing: -.12em;
  pointer-events: none;
}

.physics-hero-copy { position: relative; z-index: 2; }
.physics-hero h1 { max-width: 11ch; font-size: clamp(3.7rem, 7.6vw, 8rem); }
.physics-hero-copy > p:last-child { max-width: 47rem; margin: 2rem 0 0; color: var(--muted); font-size: clamp(1rem, 1.6vw, 1.25rem); line-height: 1.75; }

.physics-orbit {
  position: absolute;
  top: 7%;
  right: 5%;
  width: min(34vw, 420px);
  aspect-ratio: 1;
  border: 1px solid rgba(93, 231, 242, .22);
  border-radius: 50%;
  transform: rotate(-18deg);
}
.physics-orbit::before, .physics-orbit::after, .physics-orbit i { content: ""; position: absolute; inset: 15%; border: 1px solid rgba(255, 202, 97, .2); border-radius: 50%; transform: rotate(61deg); }
.physics-orbit::after { inset: 31%; border-color: rgba(146, 144, 255, .25); }
.physics-orbit i:nth-child(1) { inset: 48% auto auto -5px; width: 10px; height: 10px; border: 0; background: var(--physics-blue); box-shadow: 0 0 24px var(--physics-blue); }
.physics-orbit i:nth-child(2) { inset: 18% 13% auto auto; width: 7px; height: 7px; border: 0; background: var(--physics-amber); box-shadow: 0 0 20px var(--physics-amber); }
.physics-orbit i:nth-child(3) { inset: auto 33% 2% auto; width: 8px; height: 8px; border: 0; background: var(--physics-violet); box-shadow: 0 0 20px var(--physics-violet); }
.physics-orbit span { position: absolute; inset: calc(50% - 9px); border-radius: 50%; background: #fff; box-shadow: 0 0 32px 9px rgba(93, 231, 242, .42); }

.physics-stats { position: relative; z-index: 2; display: grid; grid-template-columns: repeat(3, 1fr); align-self: end; margin: 0; border-top: 1px solid var(--line); }
.physics-stats div { padding: 1.2rem .5rem 0; border-right: 1px solid var(--line); }
.physics-stats div:last-child { border: 0; }
.physics-stats dt { color: var(--physics-amber); font: 700 clamp(1.5rem, 3vw, 2.5rem)/1 "JetBrains Mono", monospace; }
.physics-stats dd { margin: .45rem 0 0; color: var(--muted); font-size: .75rem; text-transform: uppercase; letter-spacing: .08em; }

.physics-toolbar {
  position: sticky;
  top: 72px;
  z-index: 15;
  display: grid;
  grid-template-columns: minmax(280px, 1fr) auto auto auto minmax(82px, auto);
  align-items: end;
  gap: .75rem;
  margin: 2rem 0 5rem;
  padding: 1rem;
  border: 1px solid var(--line);
  background: rgba(9, 8, 21, .92);
  backdrop-filter: blur(18px);
}
.physics-search span { display: block; margin: 0 0 .4rem; color: var(--muted); font: 600 .65rem/1 "JetBrains Mono", monospace; text-transform: uppercase; letter-spacing: .09em; }
.physics-search input { width: 100%; height: 44px; padding: 0 .9rem; border: 1px solid var(--line); outline: 0; color: var(--ink); background: #090916; font: inherit; }
.physics-search input:focus { border-color: var(--physics-blue); box-shadow: 0 0 0 2px rgba(93, 231, 242, .12); }
.physics-filters { display: flex; gap: 1px; padding: 1px; background: var(--line); }
.physics-filters button, .physics-reset { height: 42px; min-width: 42px; padding: 0 .75rem; border: 0; color: var(--muted); background: var(--panel); font: 700 .75rem "JetBrains Mono", monospace; cursor: pointer; }
.physics-filters button:hover, .physics-filters button[aria-pressed="true"] { color: #081014; background: var(--physics-blue); }
.physics-exam-filters button:hover, .physics-exam-filters button[aria-pressed="true"] { background: var(--physics-amber); }
.physics-reset { border: 1px solid var(--line); }
.physics-reset:hover { color: var(--ink); border-color: var(--physics-violet); }
.physics-result { align-self: center; min-width: 82px; color: var(--physics-blue); font: 700 .75rem "JetBrains Mono", monospace; text-align: right; }

.physics-grade { margin-top: 6rem; }
.physics-grade > header { display: grid; grid-template-columns: 5rem 1fr; gap: 1.5rem; align-items: start; margin-bottom: 2rem; }
.physics-grade > header > span { padding-top: .35rem; color: var(--physics-amber); font: 700 .8rem "JetBrains Mono", monospace; }
.physics-grade > header p { margin: 0 0 .45rem; color: var(--physics-blue); font: 700 .72rem "JetBrains Mono", monospace; text-transform: uppercase; letter-spacing: .14em; }
.physics-grade > header h2 { max-width: 21ch; margin: 0; font-size: clamp(2rem, 4.2vw, 4.5rem); line-height: 1; letter-spacing: -.045em; }
.physics-chapters { border-top: 1px solid var(--line); }
.physics-chapter { border-bottom: 1px solid var(--line); }
.physics-chapter[hidden], .physics-grade[hidden], [data-physics-topic][hidden] { display: none; }
.physics-chapter summary { display: grid; grid-template-columns: 5rem minmax(0, 1fr) auto 2rem; gap: 1.5rem; align-items: center; min-height: 112px; padding: 1rem 0; list-style: none; cursor: pointer; }
.physics-chapter summary::-webkit-details-marker { display: none; }
.physics-chapter summary:hover .physics-chapter-title strong { color: var(--physics-blue); }
.physics-chapter-number { color: var(--muted); font: 600 .8rem "JetBrains Mono", monospace; }
.physics-chapter-title { display: grid; gap: .45rem; }
.physics-chapter-title strong { font-size: clamp(1.15rem, 2vw, 1.65rem); transition: color 160ms ease; }
.physics-chapter-title small { color: var(--muted); }
.physics-exam-tags { display: flex; gap: .45rem; }
.physics-exam-tags i { padding: .35rem .5rem; border: 1px solid rgba(93, 231, 242, .28); color: var(--physics-blue); font: 700 .65rem "JetBrains Mono", monospace; font-style: normal; }
.physics-exam-tags i + i { border-color: rgba(255, 202, 97, .3); color: var(--physics-amber); }
.physics-chevron { width: 11px; height: 11px; border-right: 2px solid var(--muted); border-bottom: 2px solid var(--muted); transform: rotate(45deg); transition: transform 160ms ease; }
.physics-chapter[open] .physics-chevron { transform: rotate(225deg); }
.physics-chapter-body { display: grid; grid-template-columns: minmax(0, 1fr) 14rem; gap: 3rem; padding: 0 0 2.5rem 6.5rem; }
.physics-topic-list { display: grid; grid-template-columns: 1fr 1fr; gap: 1px; background: var(--line); }
.physics-topic-list a { min-height: 74px; display: grid; grid-template-columns: 3rem 1fr auto; gap: .75rem; align-items: center; padding: 1rem; background: var(--panel); text-decoration: none; }
.physics-topic-list a:hover { background: var(--panel-2); }
.physics-topic-list span { color: var(--physics-amber); font: 600 .7rem "JetBrains Mono", monospace; }
.physics-topic-list strong { font-size: .9rem; line-height: 1.35; }
.physics-topic-list i { color: var(--muted); font-style: normal; }
.physics-open-chapter { align-self: end; display: flex; justify-content: space-between; gap: 1rem; padding: 1rem 0; border-bottom: 1px solid var(--physics-blue); color: var(--physics-blue); font-weight: 700; text-decoration: none; }
.physics-empty { padding: 5rem; border: 1px dashed var(--line); text-align: center; }
.physics-empty strong { font-size: 1.7rem; }
.physics-empty p { color: var(--muted); }

.auth-shell { min-height: calc(100vh - 72px); display: grid; place-items: center; padding: 2rem; }
.auth-card { width: min(460px, 100%); padding: clamp(2rem, 5vw, 4rem); border: 1px solid var(--line); background: var(--panel); }
.auth-card h1 { font-size: clamp(2rem, 6vw, 3.5rem); line-height: 1; }
.auth-card label { display: block; margin: 1.2rem 0 0.45rem; color: var(--muted); }
.auth-card input { width: 100%; padding: 0.9rem 1rem; color: var(--ink); border: 1px solid var(--line); background: #090916; font: inherit; }
.auth-card button[type="submit"] { width: 100%; margin-top: 1.5rem; padding: 1rem; border: 0; color: #071014; background: var(--cyan); font-weight: 800; cursor: pointer; }
.form-error { color: #ff8ca5; }

@media (max-width: 720px) {
  .site-header { padding: 0 1.25rem; }
  .site-header nav span { display: none; }
  .hero { min-height: 45vh; padding-inline: 1.25rem; }
  .page-card, .empty-state { grid-column: span 12; min-height: 230px; padding: 2rem 1.25rem; }
  .content-shell, .lesson-shell { width: min(100% - 2.5rem, 820px); padding-top: 2rem; }
  .breadcrumb { margin-bottom: 3rem; }
  .lesson-list a { grid-template-columns: 2.5rem 1fr; }
  .lesson-list small { grid-column: 2; }
  .physics-catalog { width: min(100% - 1rem, 1320px); padding-top: .5rem; }
  .physics-hero { min-height: 560px; grid-template-columns: 1fr; gap: 2rem; padding: 2.5rem 1.25rem; }
  .physics-hero h1 { font-size: clamp(3rem, 15vw, 5.5rem); }
  .physics-orbit { width: 75vw; top: 9%; right: -25%; opacity: .55; }
  .physics-stats { width: 100%; }
  .physics-toolbar { top: 61px; grid-template-columns: 1fr; margin: 1rem 0 3rem; }
  .physics-filters { width: 100%; }
  .physics-filters button { flex: 1; }
  .physics-result { position: absolute; right: 1rem; bottom: -1.9rem; }
  .physics-grade { margin-top: 4rem; }
  .physics-grade > header { grid-template-columns: 2.5rem 1fr; gap: .5rem; }
  .physics-chapter summary { grid-template-columns: 2.5rem 1fr 1rem; gap: .5rem; min-height: 94px; }
  .physics-exam-tags { display: none; }
  .physics-chapter-body { grid-template-columns: 1fr; gap: 1.5rem; padding: 0 0 2rem; }
  .physics-topic-list { grid-template-columns: 1fr; }
}