:root {
  --paper: #f3f6fa;
  --ink: #1b2437;
  --graphite: #4a5968;
  --line: #d5dee8;
  --sheet: #ffffff;
  --sorted: #d7efe6;
  --key: #f8d9d2;
  --mark: #0f6e56;
  --warn: #b43322;
  --focus: #1d4e89;
  --sans: "Atkinson Hyperlegible", "Segoe UI", sans-serif;
  --serif: "Newsreader", "Iowan Old Style", Georgia, serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1.0625rem;
  line-height: 1.55;
}

:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

a { color: var(--focus); }
a:hover { color: var(--ink); }

.skip {
  position: absolute;
  left: 1rem;
  top: -4rem;
  background: var(--ink);
  color: white;
  padding: 0.4rem 0.7rem;
}
.skip:focus { top: 0.5rem; }

header.site {
  position: sticky;
  top: 0;
  z-index: 5;
  background: rgba(243, 246, 250, 0.94);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(8px);
}

.bar {
  max-width: 1080px;
  margin: 0 auto;
  padding: 0.85rem 1.25rem 0.7rem;
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 0.35rem 1.15rem;
}

.wordmark {
  font-family: var(--serif);
  font-weight: 650;
  font-size: 1.45rem;
  color: var(--ink);
  text-decoration: none;
  margin-right: 0.4rem;
}
.wordmark:hover { color: var(--ink); }

.nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.15rem 0.95rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.nav a {
  color: var(--graphite);
  text-decoration: none;
  font-size: 0.98rem;
}
.nav a:hover { color: var(--ink); }
.nav a[aria-current="page"] {
  color: var(--mark);
  box-shadow: inset 0 -2px 0 var(--mark);
}

main {
  max-width: 1080px;
  margin: 0 auto;
  padding: 1.6rem 1.25rem 4rem;
}

.prose { max-width: 68ch; }

h1, h2, h3, .sheet {
  scroll-margin-top: 4.75rem;
}

h1, h2, h3 {
  font-family: var(--serif);
  font-weight: 650;
  letter-spacing: -0.015em;
  line-height: 1.15;
}

h1 { font-size: 2.5rem; margin: 0 0 0.45rem; }
h2 { font-size: 1.65rem; margin: 2rem 0 0.45rem; }
h3 { font-size: 1.25rem; margin: 1.4rem 0 0.35rem; }

.lede {
  font-family: var(--serif);
  font-size: 1.35rem;
  line-height: 1.35;
  max-width: 34ch;
  margin: 0 0 1.25rem;
}

p { margin: 0.7rem 0; }

.prose ol, .prose ul { padding-left: 1.2rem; }
.prose li { margin: 0.28rem 0; }

table {
  border-collapse: collapse;
  margin: 1rem 0 1.2rem;
  font-size: 0.98rem;
  max-width: 100%;
}
th, td {
  text-align: left;
  padding: 0.42rem 0.75rem 0.42rem 0;
  border-bottom: 1px solid var(--line);
  vertical-align: top;
}
th { font-weight: 700; }

.code, pre.code {
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  font-size: 0.92rem;
  line-height: 1.45;
  background: var(--sheet);
  border: 1px solid var(--line);
  border-left: 3px solid var(--ink);
  padding: 0.8rem 1rem;
  overflow-x: auto;
  max-width: 68ch;
}

.call {
  max-width: 68ch;
  margin: 1.1rem 0;
  padding: 0.15rem 0 0.15rem 0.9rem;
  border-left: 3px solid var(--mark);
}
.call.warn { border-left-color: var(--warn); }
.call strong { font-family: var(--serif); font-size: 1.08rem; }

.next-note {
  margin-top: 2.2rem;
  max-width: 68ch;
  padding-top: 0.8rem;
  border-top: 1px solid var(--line);
}

.sheet {
  margin-top: 1.4rem;
  background: var(--sheet);
  border: 1px solid var(--line);
  border-top: 4px solid var(--ink);
  padding: 1rem 1rem 1.15rem;
  max-width: 920px;
}

.sheet h2 {
  margin-top: 0;
  font-size: 1.45rem;
}

.controls, .presets, .modes {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  align-items: center;
  margin: 0.55rem 0 0.8rem;
}

button, .file-link {
  font-family: var(--sans);
  font-size: 1rem;
  background: var(--ink);
  color: white;
  border: 1px solid var(--ink);
  padding: 0.45rem 0.75rem;
  cursor: pointer;
  text-decoration: none;
  display: inline-block;
}
button:hover, .file-link:hover { background: #2a3854; color: white; }
button[aria-pressed="true"] {
  background: var(--mark);
  border-color: var(--mark);
}
button.quiet {
  background: transparent;
  color: var(--ink);
}
button.quiet:hover { background: var(--paper); color: var(--ink); }

label.field {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  align-items: center;
  margin: 0.4rem 0 0.8rem;
}
input[type="text"], input[type="range"] {
  font-family: var(--sans);
  font-size: 1rem;
  color: var(--ink);
  border: 1px solid var(--graphite);
  background: white;
  padding: 0.4rem 0.5rem;
}
input[type="text"] { min-width: min(100%, 16rem); }

.array {
  display: flex;
  flex-wrap: wrap;
  align-items: flex-end;
  gap: 0.35rem;
  min-height: 6.2rem;
  margin: 0.4rem 0 0.2rem;
}

.slot { display: flex; flex-direction: column; align-items: center; width: 3.35rem; }
.badge {
  min-height: 1.15rem;
  font-size: 0.78rem;
  color: var(--warn);
  font-weight: 700;
}
.cell {
  width: 3.15rem;
  height: 3.15rem;
  display: grid;
  place-items: center;
  border: 1px solid var(--ink);
  background: white;
  font-size: 1.2rem;
  font-variant-numeric: tabular-nums;
}
.cell.sorted { background: var(--sorted); }
.cell.key { background: var(--key); }
.cell.hole { background: transparent; border-style: dashed; color: transparent; }
.cell.hot { box-shadow: inset 0 0 0 2px var(--ink); }
.idx { font-size: 0.78rem; color: var(--graphite); margin-top: 0.2rem; }

.wall {
  width: 3px;
  height: 3.15rem;
  background: var(--warn);
  align-self: center;
  margin-bottom: 1.15rem;
}

.says {
  min-height: 3.2rem;
  max-width: 68ch;
  margin: 0.8rem 0 0.3rem;
}
.meta {
  color: var(--graphite);
  font-size: 0.95rem;
  margin: 0.2rem 0;
}

.chart-wrap { width: 100%; overflow-x: auto; }
.chart-wrap svg { width: min(100%, 680px); height: auto; display: block; }
.series-toggle[aria-pressed="false"] { opacity: 0.45; }

.path {
  list-style: none;
  padding: 0;
  margin: 1.4rem 0 0;
  max-width: 68ch;
  counter-reset: note;
}
.path li {
  counter-increment: note;
  padding: 0.9rem 0;
  border-top: 1px solid var(--line);
}
.path a {
  display: block;
  font-family: var(--serif);
  font-size: 1.35rem;
  font-weight: 650;
  line-height: 1.2;
  text-decoration: none;
  color: var(--ink);
}
.path a::before {
  content: counter(note) ". ";
  color: var(--mark);
}
.path a:hover { color: var(--focus); }
.path span { display: block; color: var(--graphite); margin-top: 0.25rem; }

details.answer { max-width: 68ch; margin: 0.8rem 0 1.2rem; }
details.answer summary {
  cursor: pointer;
  font-weight: 700;
  color: var(--mark);
}
details.answer summary:hover { color: var(--ink); }

.question { max-width: 72ch; padding-bottom: 0.4rem; border-bottom: 1px solid var(--line); margin-bottom: 1.2rem; }

.videos { display: grid; gap: 1.4rem; max-width: 760px; }
.video-frame {
  position: relative;
  padding-top: 56.25%;
  background: var(--ink);
}
.video-frame iframe {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: 0;
}

.file-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin: 0.8rem 0 1.2rem;
}

.crib {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.5rem 2.5rem;
  max-width: 920px;
  align-items: start;
}
.crib h2 { margin-top: 1.1rem; }
.crib h2:first-child { margin-top: 0; }
@media (max-width: 720px) {
  .crib { grid-template-columns: 1fr; }
}

.result { min-height: 1.4rem; font-weight: 700; }
.result.ok { color: var(--mark); }
.result.bad { color: var(--warn); }

.katex-display { overflow-x: auto; overflow-y: hidden; }

footer.site-foot {
  max-width: 1080px;
  margin: 0 auto;
  padding: 0 1.25rem 2rem;
  color: var(--graphite);
  font-size: 0.95rem;
}

@media (max-width: 640px) {
  h1 { font-size: 2.05rem; }
  .slot { width: 2.7rem; }
  .cell { width: 2.55rem; height: 2.55rem; font-size: 1rem; }
  .wall { height: 2.55rem; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}

@media print {
  header.site, .controls, .presets, .modes, .file-row, footer.site-foot, .next-note { display: none !important; }
  body { background: white; }
  .sheet { border: 1px solid #ccc; }
}