/* Shared tokens and components for every page of Optimization in Action.
 * Palette and type follow MIT's core identity: MIT Red #750014, Bright Red #ff1423,
 * Silver Gray #8b959e, black and white, set in Neue Haas Grotesk (Helvetica / Arimo fallback). */
:root {
  color-scheme: light;
  --font-sans: "Neue Haas Grotesk Text", "Neue Haas Grotesk Display", "Helvetica Neue", Helvetica, Arimo, Arial, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, "SFMono-Regular", Menlo, monospace;
  --mit-red: #750014;
  --mit-bright: #ff1423;
  --mit-silver: #8b959e;
  --bg: #f4f5f6;
  --surface: #ffffff;
  --surface2: #eef0f2;
  --ink: #000000;
  --ink2: #3b4046;
  --muted: #69727a;
  --grid: #e2e5e8;
  --axis: #b8bfc5;
  --border: rgba(0, 0, 0, 0.14);
  --accent: #750014;
  --accent-text: #750014;
  --pine: #000000;
  --pine-text: #000000;
  --on-solid: #ffffff;
  --c-blue: #000000;
  --c-aqua: #8b959e;
  --c-violet: #ff1423;
  --good: #0ca30c;
  --good-text: #006300;
  --crit: #d0101f;
  --region: rgba(139, 149, 158, 0.22);
  --sel: rgba(117, 0, 20, 0.07);
  --halo: rgba(255, 255, 255, 0.88);
  --bar-bg: rgba(255, 255, 255, 0.92);
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    color-scheme: dark;
    --bg: #000000; --surface: #111214; --surface2: #1b1d20;
    --ink: #ffffff; --ink2: #c9ced3; --muted: #8b959e;
    --grid: #25282c; --axis: #3d4247; --border: rgba(255, 255, 255, 0.14);
    --accent: #ff1423; --accent-text: #ff5a64;
    --pine: #ffffff; --pine-text: #ffffff; --on-solid: #000000;
    --c-blue: #ffffff; --c-aqua: #a7b0b8; --c-violet: #ff4d57;
    --good: #0ca30c; --good-text: #4fc04f; --crit: #ff6b73;
    --region: rgba(139, 149, 158, 0.24); --sel: rgba(255, 20, 35, 0.12);
    --halo: rgba(17, 18, 20, 0.88);
    --bar-bg: rgba(0, 0, 0, 0.9);
  }
}
:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #000000; --surface: #111214; --surface2: #1b1d20;
  --ink: #ffffff; --ink2: #c9ced3; --muted: #8b959e;
  --grid: #25282c; --axis: #3d4247; --border: rgba(255, 255, 255, 0.14);
  --accent: #ff1423; --accent-text: #ff5a64;
  --pine: #ffffff; --pine-text: #ffffff; --on-solid: #000000;
  --c-blue: #ffffff; --c-aqua: #a7b0b8; --c-violet: #ff4d57;
  --good: #0ca30c; --good-text: #4fc04f; --crit: #ff6b73;
  --region: rgba(139, 149, 158, 0.24); --sel: rgba(255, 20, 35, 0.12);
  --halo: rgba(17, 18, 20, 0.88);
  --bar-bg: rgba(0, 0, 0, 0.9);
}

html.i18n-loading body { visibility: hidden; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: 15.5px;
  line-height: 1.55;
  padding-inline: 16px;
  padding-block: 0 48px;
}
*, *::before, *::after { box-sizing: border-box; }
a { color: var(--accent-text); }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* ---- top bar (every page) ---- */
.topbar {
  position: sticky; top: env(safe-area-inset-top, 0px); z-index: 20;
  margin-inline: -16px; padding: 10px 16px;
  background: #000000; color: #ffffff;
  border-bottom: 3px solid var(--mit-red);
}
.topbar-in {
  max-width: 1080px; margin: 0 auto;
  display: flex; align-items: center; gap: 12px 18px; flex-wrap: wrap;
}
.brand {
  font-family: var(--font-sans);
  font-weight: 700; font-size: 17px; letter-spacing: -0.005em;
  color: #ffffff; text-decoration: none; display: inline-flex; align-items: center; gap: 9px;
}
.brand-mark {
  width: 22px; height: 22px; border-radius: 0; background: var(--accent); flex: none;
  display: grid; place-items: center; color: var(--on-solid);
  font: 600 12px var(--font-mono);
}
.topnav { display: flex; gap: 4px; flex-wrap: wrap; }
.topnav a {
  font-size: 14px; font-weight: 600; color: #c9ced3; text-decoration: none;
  padding: 6px 10px; border-radius: 0;
}
.topnav a:hover { background: #1b1d20; color: #ffffff; }
.backlink {
  font-size: 14px; font-weight: 600; color: #ffffff; text-decoration: none;
  display: inline-flex; align-items: center; gap: 6px;
}
.backlink:hover { color: #c9ced3; }
.lang { margin-left: auto; display: inline-flex; align-items: center; gap: 8px; }
.lang-label {
  font-family: var(--font-mono); font-size: 10.5px;
  letter-spacing: 0.12em; text-transform: uppercase; color: #8b959e;
}
@media (max-width: 640px) {
  .topbar { position: static; }
  .topnav { order: 3; width: 100%; margin-inline: -10px; }
  .lang-label { display: none; }
}
.lang-select {
  font: 600 13.5px var(--font-sans); color: #ffffff; color-scheme: dark;
  background: #1b1d20; border: 1px solid #3d4247; border-radius: 0;
  padding: 6px 8px; cursor: pointer;
}

/* ---- page scaffolding ---- */
.wrap { max-width: 1060px; margin: 0 auto; display: flex; flex-direction: column; gap: 22px; }
header.masthead { padding-block: 30px 4px; }
.eyebrow {
  font-family: var(--font-mono);
  font-size: 11.5px; letter-spacing: 0.14em; text-transform: uppercase;
  color: var(--accent-text); margin: 0 0 10px;
}
.eyebrow b { color: var(--ink); font-weight: 600; }
h1 {
  font-family: var(--font-sans);
  font-weight: 700; font-size: clamp(34px, 6vw, 52px); line-height: 1.02;
  margin: 0 0 12px; letter-spacing: -0.025em; text-wrap: balance;
}
.lede { max-width: 64ch; color: var(--ink2); margin: 0; }
.lede strong { color: var(--ink); }

.card { background: var(--surface); border: 1px solid var(--border); border-radius: 4px; padding: 16px; }
.card h2, h2.plain {
  font-family: var(--font-sans); font-weight: 600;
  font-size: 17px; margin: 0 0 10px; letter-spacing: 0.005em;
}
.kicker {
  display: block; font-family: var(--font-mono); font-weight: 400;
  font-size: 10.5px; letter-spacing: 0.13em; text-transform: uppercase; color: var(--muted);
  margin-bottom: 3px;
}

details { border: 1px solid var(--border); border-radius: 4px; background: var(--surface); overflow: hidden; }
details + details { margin-top: 10px; }
summary {
  cursor: pointer; padding: 13px 16px; font-weight: 600; font-size: 14.5px; list-style: none;
  display: flex; align-items: center; gap: 10px;
}
summary::-webkit-details-marker { display: none; }
summary::before { content: "+"; font-family: var(--font-mono); color: var(--accent-text); font-weight: 600; }
details[open] summary::before { content: "\2212"; }
details .body { padding: 0 16px 15px; color: var(--ink2); font-size: 14.5px; max-width: 72ch; }
details .body p { margin: 0 0 9px; }
details .body p:last-child { margin-bottom: 0; }
.formula {
  font-family: var(--font-mono); font-size: 13px; background: var(--surface2);
  border: 1px solid var(--border); border-radius: 3px; padding: 10px 13px; margin: 8px 0;
  overflow-x: auto; white-space: pre; line-height: 1.7; color: var(--ink);
}
.note { font-size: 13px; color: var(--muted); max-width: 78ch; margin: 0; }

@media (prefers-reduced-motion: reduce) { * { transition: none !important; scroll-behavior: auto !important; } }