/* z-stackr — site stylesheet.
 *
 * Theme "Lightbox": the cool white of a macro light tent, near-black ink, and
 * one accent, the green of a camera's focus peaking. Light by default, dark
 * when the visitor's system asks for it. No web fonts, no external resources.
 * Every colour below is a token; new rules use the tokens only.
 */

:root {
  --paper: #f3f5f6;
  --paper-2: #e7ebed;
  --paper-3: #ffffff;
  --ink: #111417;
  --ink-2: #4f5861;
  --rule: #cfd6db;
  --accent: #067a52;          /* text and links on the page */
  --accent-bright: #19c37d;   /* marks, bars, focus rings */
  --accent-wash: rgba(25, 195, 125, 0.12);
  --on-accent: #ffffff;
  --code-bg: #e9eef0;
  --shadow: 0 1px 2px rgba(17, 20, 23, 0.06), 0 6px 18px rgba(17, 20, 23, 0.06);

  --font-sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, "Cascadia Mono", "SF Mono", Consolas, "Liberation Mono", monospace;
  --measure: 46rem;
  --wide: 72rem;
  color-scheme: light dark;
}

@media (prefers-color-scheme: dark) {
  :root {
    --paper: #0e1113;
    --paper-2: #161a1d;
    --paper-3: #1b2024;
    --ink: #e9edef;
    --ink-2: #9aa5ad;
    --rule: #2a3137;
    --accent: #3fd696;
    --accent-bright: #2fd28c;
    --accent-wash: rgba(47, 210, 140, 0.12);
    --on-accent: #06140e;
    --code-bg: #12171a;
    --shadow: none;
  }
}

*, *::before, *::after { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 5rem; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: 1.0625rem;
  line-height: 1.62;
  -webkit-text-size-adjust: 100%;
}

img { max-width: 100%; height: auto; display: block; }

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 0.18em; }
a:hover { text-decoration-thickness: 2px; }
a:focus-visible, button:focus-visible, summary:focus-visible {
  outline: 2px solid var(--accent-bright);
  outline-offset: 2px;
}

.container { width: 100%; max-width: var(--wide); margin: 0 auto; padding: 0 1.25rem; }

/* ── Masthead ─────────────────────────────────────────────────────────── */

.masthead {
  position: sticky;
  top: 0;
  z-index: 20;
  background: color-mix(in srgb, var(--paper) 92%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--rule);
}

/* The focus ladder: thin bars that sharpen from left to right, a stack of
   slices coming into focus. */
.masthead::after {
  content: "";
  display: block;
  height: 3px;
  background: linear-gradient(90deg,
    transparent 0%,
    color-mix(in srgb, var(--accent-bright) 18%, transparent) 20%,
    color-mix(in srgb, var(--accent-bright) 45%, transparent) 45%,
    var(--accent-bright) 70%,
    var(--accent-bright) 100%);
}

.masthead .container {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  min-height: 3.5rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  color: var(--ink);
  text-decoration: none;
  font-weight: 700;
  letter-spacing: -0.01em;
  white-space: nowrap;
}
.brand svg { width: 22px; height: 22px; }
.brand .z { color: var(--accent); }

.masthead nav { display: flex; flex-wrap: wrap; gap: 0.25rem 1.1rem; font-size: 0.95rem; }
.masthead nav a { color: var(--ink-2); text-decoration: none; padding: 0.15rem 0; border-bottom: 2px solid transparent; }
.masthead nav a:hover { color: var(--ink); }
.masthead nav a[aria-current="page"] { color: var(--ink); border-bottom-color: var(--accent-bright); }

/* ── Page head ────────────────────────────────────────────────────────── */

main.container { padding-top: 2.5rem; padding-bottom: 4rem; }

.page-head { margin-bottom: 2.25rem; }
.eyebrow {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 0 0 0.6rem;
}
h1 {
  font-size: clamp(2.1rem, 4.5vw, 3.2rem);
  line-height: 1.08;
  letter-spacing: -0.025em;
  margin: 0 0 0.75rem;
}
.subtitle { font-size: 1.2rem; color: var(--ink-2); max-width: var(--measure); margin: 0 0 1.25rem; }

.cta-row { display: flex; flex-wrap: wrap; gap: 0.75rem; margin: 1.5rem 0 0; }
.cta {
  display: inline-block;
  background: var(--ink);
  color: var(--paper);
  padding: 0.65rem 1.1rem;
  border-radius: 6px;
  text-decoration: none;
  font-weight: 600;
}
.cta:hover { background: var(--accent); color: var(--on-accent); }
.cta-secondary { background: transparent; color: var(--ink); border: 1px solid var(--rule); }
.cta-secondary:hover { background: var(--paper-2); color: var(--ink); }

/* ── Sections ─────────────────────────────────────────────────────────── */

main > section { margin: 3.5rem 0 0; }
main > section > :where(p, ul, ol, .status, .code-block, h3, dl) { max-width: var(--measure); }

h2 {
  font-size: 1.6rem;
  line-height: 1.2;
  letter-spacing: -0.015em;
  margin: 0 0 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--rule);
  display: flex;
  align-items: baseline;
  gap: 0.8rem;
}
.sec-num {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--accent);
  letter-spacing: 0.04em;
}
h3 { font-size: 1.15rem; margin: 2rem 0 0.5rem; }

p, ul, ol { margin: 0 0 1rem; }
li { margin: 0.25rem 0; }
.small { font-size: 0.92rem; color: var(--ink-2); }
.more { font-size: 0.95rem; }
.more a { font-weight: 600; }

code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: var(--code-bg);
  padding: 0.08em 0.35em;
  border-radius: 4px;
}

/* ── Intro grid ───────────────────────────────────────────────────────── */

.intro-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1.25fr);
  gap: 2.5rem;
  align-items: start;
}
.intro-grid p { max-width: none; }

/* ── Cards ────────────────────────────────────────────────────────────── */

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(16rem, 1fr));
  gap: 1rem;
}
.card {
  display: block;
  background: var(--paper-3);
  border: 1px solid var(--rule);
  border-radius: 8px;
  padding: 1.1rem 1.2rem 1rem;
  color: var(--ink);
  text-decoration: none;
  box-shadow: var(--shadow);
  position: relative;
}
.card::before {
  content: "";
  position: absolute;
  left: 1.2rem; right: 1.2rem; top: 0;
  height: 2px;
  background: var(--accent-bright);
  transform: scaleX(0.18);
  transform-origin: left;
  transition: transform 160ms ease;
}
a.card:hover::before { transform: scaleX(1); }
.card h3 { margin: 0.2rem 0 0.4rem; font-size: 1.05rem; }
.card p { margin: 0; color: var(--ink-2); font-size: 0.95rem; }

/* ── Figures ──────────────────────────────────────────────────────────── */

.fig { margin: 1.5rem 0; }
.fig > a, .fig > img, .fig .frame {
  display: block;
  background: var(--paper-2);
  border: 1px solid var(--rule);
  border-radius: 8px;
  padding: 8px;
}
.fig img { border-radius: 4px; }
figcaption, .fig-note { font-size: 0.9rem; color: var(--ink-2); margin-top: 0.55rem; max-width: var(--measure); }
figcaption .fig-label { font-family: var(--font-mono); font-size: 0.82rem; color: var(--accent); margin-right: 0.35rem; }

.fig-grid { display: grid; grid-template-columns: var(--fig-cols, 1fr 1fr); gap: 1rem; align-items: start; }
.fig-grid .fig { margin: 0; }
.fig-portrait { max-width: var(--fig-max, 520px); margin-left: auto; margin-right: auto; }

/* Before / after slider */
.compare { position: relative; overflow: hidden; border-radius: 4px; user-select: none; touch-action: pan-y; }
.compare img { width: 100%; }
.compare .after { position: absolute; inset: 0; clip-path: inset(0 0 0 var(--split, 50%)); }
.compare .handle {
  position: absolute; top: 0; bottom: 0; left: var(--split, 50%);
  width: 2px; margin-left: -1px; background: var(--accent-bright);
  pointer-events: none;
}
.compare .handle::after {
  content: "\2194";
  position: absolute; top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  width: 2rem; height: 2rem; border-radius: 50%;
  background: var(--accent-bright); color: var(--on-accent);
  display: grid; place-items: center; font-size: 1rem;
}
.compare .tag {
  position: absolute; top: 0.6rem;
  font-family: var(--font-mono); font-size: 0.75rem; letter-spacing: 0.06em;
  background: rgba(17, 20, 23, 0.72); color: #fff; padding: 0.15rem 0.45rem; border-radius: 3px;
}
.compare .tag.left { left: 0.6rem; }
.compare .tag.right { right: 0.6rem; }
.compare input[type="range"] {
  position: absolute; inset: 0; width: 100%; height: 100%;
  opacity: 0; cursor: ew-resize; margin: 0;
}

/* Diagrams (inline SVG) */
.diagram { width: 100%; height: auto; display: block; }
.diagram text { font-family: var(--font-mono); font-size: 12.5px; fill: var(--ink); }
.diagram .lbl { font-size: 11px; fill: var(--ink-2); letter-spacing: 0.06em; }
.diagram .muted { fill: var(--ink-2); }
.diagram .box { fill: var(--paper-3); stroke: var(--rule); stroke-width: 1; }
.diagram .box-accent { fill: var(--accent-wash); stroke: var(--accent-bright); stroke-width: 1.2; }
.diagram .arrow { fill: none; stroke: var(--accent-bright); stroke-width: 1.6; }
.diagram .head { fill: var(--accent-bright); }
.diagram .thin { fill: none; stroke: var(--ink-2); stroke-width: 1; }

/* ── Tables ───────────────────────────────────────────────────────────── */

.table-wrap { overflow-x: auto; margin: 1rem 0 1.25rem; }
table { border-collapse: collapse; width: 100%; font-size: 0.95rem; }
th, td { text-align: left; vertical-align: top; padding: 0.5rem 0.75rem; border-bottom: 1px solid var(--rule); }
thead th { font-size: 0.8rem; font-family: var(--font-mono); letter-spacing: 0.05em; text-transform: uppercase; color: var(--ink-2); border-bottom: 2px solid var(--ink); }
tbody tr:hover { background: var(--accent-wash); }
td code { white-space: nowrap; }

/* ── Callouts ─────────────────────────────────────────────────────────── */

.status {
  border-left: 3px solid var(--accent-bright);
  background: var(--paper-2);
  padding: 0.85rem 1.1rem;
  border-radius: 0 6px 6px 0;
  margin: 1.25rem 0;
}
.status-label {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  color: var(--accent);
  margin-bottom: 0.25rem;
}
.status p:last-child { margin-bottom: 0; }

/* ── Code blocks ──────────────────────────────────────────────────────── */

.code-block { border: 1px solid var(--rule); border-radius: 8px; overflow: hidden; margin: 1rem 0 1.25rem; background: var(--code-bg); }
.code-block-head {
  display: flex; justify-content: space-between; align-items: center;
  font-family: var(--font-mono); font-size: 0.78rem; color: var(--ink-2);
  padding: 0.4rem 0.75rem; border-bottom: 1px solid var(--rule); background: var(--paper-2);
}
.copy-btn {
  font: inherit; color: var(--ink); background: var(--paper-3);
  border: 1px solid var(--rule); border-radius: 4px; padding: 0.1rem 0.55rem; cursor: pointer;
}
.copy-btn:hover { border-color: var(--accent-bright); }
.code-block pre { margin: 0; padding: 0.85rem 1rem; overflow-x: auto; }
.code-block code { background: none; padding: 0; font-size: 0.88rem; line-height: 1.55; }

/* ── Key list ─────────────────────────────────────────────────────────── */

kbd {
  font-family: var(--font-mono); font-size: 0.82em;
  border: 1px solid var(--rule); border-bottom-width: 2px; border-radius: 4px;
  padding: 0.02em 0.4em; background: var(--paper-3);
  white-space: nowrap;
}

dl.defs { display: grid; grid-template-columns: max-content 1fr; gap: 0.4rem 1.25rem; }
dl.defs dt { font-weight: 600; }
dl.defs dd { margin: 0; color: var(--ink-2); }

/* ── "On this page" ───────────────────────────────────────────────────── */

.toc-side { display: none; }
.toc-inline {
  border: 1px solid var(--rule); border-radius: 8px; background: var(--paper-3);
  padding: 0.55rem 0.9rem; margin: 0 0 2rem; max-width: var(--measure);
}
.toc-inline summary { cursor: pointer; font-family: var(--font-mono); font-size: 0.85rem; color: var(--ink-2); }
.toc-inline ol, .toc-side ol { list-style: none; margin: 0.5rem 0 0; padding: 0; }
.toc-inline li, .toc-side li { margin: 0; }
.toc-inline a, .toc-side a {
  display: flex; gap: 0.6rem; padding: 0.22rem 0; color: var(--ink-2);
  text-decoration: none; font-size: 0.93rem;
}
.toc-inline a:hover, .toc-side a:hover { color: var(--ink); }
.toc-num { font-family: var(--font-mono); font-size: 0.8rem; color: var(--accent); min-width: 1.6rem; }
.toc-back {
  position: fixed; right: 1rem; bottom: 1rem; z-index: 15;
  background: var(--ink); color: var(--paper); text-decoration: none;
  font-size: 0.85rem; padding: 0.45rem 0.8rem; border-radius: 999px;
  opacity: 0; pointer-events: none; transition: opacity 150ms ease;
}
.toc-back.is-visible { opacity: 1; pointer-events: auto; }

@media (min-width: 1200px) {
  body.has-toc .masthead .container, body.has-toc footer .container { max-width: calc(var(--wide) + 16rem); }
  main.with-toc {
    max-width: calc(var(--wide) + 16rem);
    display: grid;
    grid-template-columns: 13rem minmax(0, 1fr);
    column-gap: 3rem;
  }
  main.with-toc > * { grid-column: 2; }
  main.with-toc > .toc-side {
    grid-column: 1;
    display: block;
    position: sticky; top: 5rem; align-self: start;
    max-height: calc(100vh - 6rem); overflow-y: auto;
    padding-top: 0.25rem;
  }
  .toc-head { font-family: var(--font-mono); font-size: 0.75rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--ink-2); margin: 0 0 0.25rem; }
  .toc-side a { border-left: 2px solid var(--rule); padding-left: 0.7rem; }
  .toc-side a[aria-current="location"] { color: var(--ink); border-left-color: var(--accent-bright); }
  main.with-toc > .toc-inline, .toc-back { display: none; }
}

/* ── Footer ───────────────────────────────────────────────────────────── */

footer { border-top: 1px solid var(--rule); padding: 1.5rem 0 2.5rem; font-size: 0.9rem; color: var(--ink-2); }
footer p { margin: 0.25rem 0; }
footer a { color: var(--ink-2); }
footer a:hover { color: var(--ink); }

/* ── Small screens ────────────────────────────────────────────────────── */

@media (max-width: 860px) {
  .intro-grid { grid-template-columns: 1fr; gap: 1.5rem; }
}
@media (max-width: 720px) {
  body { font-size: 1rem; }
  .masthead .container { flex-wrap: wrap; gap: 0.35rem 1rem; padding-top: 0.5rem; padding-bottom: 0.5rem; }
  .masthead nav { gap: 0.15rem 0.9rem; }
  .fig-grid { grid-template-columns: 1fr; }
  dl.defs { grid-template-columns: 1fr; }
  dl.defs dd { margin-bottom: 0.6rem; }
  main { overflow-wrap: anywhere; }
  td code { white-space: normal; }
}