*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; scroll-padding-top: 72px; }
body {
  margin: 0; background: var(--paper); color: var(--ink);
  font: 400 17px/1.62 var(--f-body); font-stretch: 100%;
  -webkit-font-smoothing: antialiased; text-rendering: optimizeLegibility;
  overflow-x: hidden;
}
img, svg { display: block; max-width: 100%; }
a { color: inherit; }
button { font: inherit; color: inherit; }
code, var, .mono { font-family: var(--f-mono); }
var { font-style: italic; font-size: 0.95em; }
code { font-size: 0.86em; }
sup, sub { line-height: 0; }
mark { background: none; color: inherit; box-shadow: inset 0 -0.42em 0 var(--tint-learner); }
::selection { background: var(--learner); color: #fff; }

.skip { position: absolute; left: -9999px; top: 8px; z-index: 100; background: var(--ink); color: var(--paper); padding: 8px 14px; border-radius: var(--radius); }
.skip:focus { left: 8px; }
:focus-visible { outline: 2px solid var(--learner); outline-offset: 3px; border-radius: 2px; }

.wrap { max-width: var(--wrap); margin: 0 auto; padding: 0 var(--gutter); }

/* ---- type ---- */
.eyebrow {
  font: 500 12px/1.4 var(--f-mono); letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--ink-3); margin: 0 0 18px; display: flex; align-items: center; gap: 10px;
}
.eyebrow::before {
  content: ''; width: 9px; height: 9px; flex: none; transform: rotate(45deg);
  border: 1.5px solid var(--learner);
}
.h2 {
  font-family: var(--f-display); font-stretch: 75%; font-weight: 750;
  font-size: clamp(30px, 4.4vw, 54px); line-height: 1.02; letter-spacing: -0.012em;
  margin: 0 0 28px; max-width: 22ch; text-wrap: balance;
}
.h3 {
  font-family: var(--f-display); font-stretch: 85%; font-weight: 700;
  font-size: 21px; line-height: 1.2; margin: 0 0 6px; letter-spacing: -0.005em;
}
.lede { font-size: clamp(17px, 1.6vw, 19px); line-height: 1.6; color: var(--ink-2); max-width: 60ch; margin: 0 0 28px; }
.lede--narrow { max-width: 68ch; margin-bottom: 40px; }
.prose p { margin: 0 0 16px; max-width: 62ch; color: var(--ink-2); }
.prose p em { color: var(--ink); font-style: normal; font-weight: 600; }
.prose-sm { font-size: 15px; color: var(--ink-2); max-width: 78ch; margin: 12px 0 8px; }
.stage__src, .figsrc, .insight__src {
  font: 400 12px/1.5 var(--f-mono); color: var(--ink-3); margin: 10px 0 0; letter-spacing: 0.01em;
}
.figsrc { margin-top: 14px; }

/* ---- buttons & controls ---- */
.btn {
  display: inline-flex; align-items: center; gap: 8px; min-height: 42px; padding: 0 18px;
  border: 1px solid var(--rule-2); border-radius: 999px; background: var(--surface);
  font: 600 14px/1 var(--f-body); text-decoration: none; cursor: pointer;
  transition: border-color .2s var(--ease), background .2s var(--ease), transform .2s var(--ease);
}
.btn:hover { border-color: var(--ink); }
.btn--solid { background: var(--ink); border-color: var(--ink); color: var(--paper); }
.btn--solid:hover { background: var(--learner); border-color: var(--learner); color: #fff; }
.linkbtn {
  background: none; border: 0; padding: 0; cursor: pointer; color: var(--ink-2);
  font: inherit; text-decoration: underline; text-decoration-color: var(--rule-2); text-underline-offset: 3px;
}
.linkbtn:hover { color: var(--ink); text-decoration-color: var(--learner); }

.seg {
  display: inline-flex; padding: 3px; gap: 2px; border-radius: 999px;
  background: var(--band); border: 1px solid var(--rule);
}
.seg button {
  border: 0; background: none; cursor: pointer; border-radius: 999px;
  padding: 6px 13px; min-height: 32px; font: 500 13px/1 var(--f-mono); color: var(--ink-2);
  transition: background .2s var(--ease), color .2s var(--ease);
}
.seg button[aria-pressed="true"] { background: var(--surface); color: var(--ink); box-shadow: 0 1px 2px rgba(15,27,45,.12); }
.seg button:hover { color: var(--ink); }

/* ---- nav ---- */
.nav {
  position: sticky; top: 0; z-index: 50; height: 60px;
  display: flex; align-items: center; gap: 24px; padding: 0 var(--gutter);
  /* Opaque, no backdrop blur: a blurred sticky bar re-rasterizes on every scroll frame. */
  background: color-mix(in srgb, var(--paper) 96%, transparent);
  border-bottom: 1px solid var(--rule);
}
.nav__brand {
  font-family: var(--f-display); font-stretch: 62%; font-weight: 900; font-size: 22px;
  letter-spacing: 0.04em; text-decoration: none;
}
.route { flex: 1; overflow-x: auto; overflow-y: hidden; scrollbar-width: none; }
.route::-webkit-scrollbar { display: none; }
.route ol {
  list-style: none; margin: 0 auto; padding: 0; display: flex; align-items: center;
  width: max-content; position: relative;
}
.route ol::before {
  content: ''; position: absolute; left: 14px; right: 14px; top: 50%; height: 1px; background: var(--rule-2);
}
.route li { position: relative; }
.route a {
  display: flex; align-items: center; gap: 7px; padding: 8px 12px; text-decoration: none;
  font: 500 12px/1 var(--f-mono); letter-spacing: 0.04em; text-transform: uppercase; color: var(--ink-3);
  background: var(--paper); border-radius: 999px;
}
.route a:hover { color: var(--ink); }
.wp { width: 8px; height: 8px; transform: rotate(45deg); border: 1.5px solid var(--rule-2); background: var(--paper); transition: all .25s var(--ease); }
.route a[aria-current="true"] { color: var(--ink); }
.route a[aria-current="true"] .wp { background: var(--learner); border-color: var(--learner); }
.theme-btn {
  width: 38px; height: 38px; display: grid; place-items: center; flex: none; cursor: pointer;
  border: 1px solid var(--rule-2); border-radius: 50%; background: var(--surface);
}
.theme-btn:hover { border-color: var(--ink); }

@media (max-width: 760px) {
  .route a { padding: 8px 8px; font-size: 0; gap: 0; }
  .route a .wp { width: 9px; height: 9px; }
  .route a[aria-current="true"] { font-size: 11px; gap: 7px; }
  .nav { gap: 12px; }
}

/* ---- reveal ---- */
.reveal { opacity: 0; transform: translateY(14px); transition: opacity .8s var(--ease), transform .8s var(--ease); }
.reveal.is-in { opacity: 1; transform: none; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .reveal { opacity: 1; transform: none; transition: none; }
  *, *::before, *::after { animation-duration: 0.001ms !important; transition-duration: 0.001ms !important; }
}