/* Design tokens, reset, page background, typography, callouts.
   Aesthetic: 3blue1brown-style holographic chalkboard — near-black blue,
   full-page fixed gridlines, nebula glows, manim-bright curve colors,
   math serif for equations. Knob colors are load-bearing:
   green = up/down (k), blue = sideways (h), yellow = stretch/flip (a). */

:root {
  --paper: #0b0d15;        /* page background */
  --paper-2: #121624;      /* elevated panels */
  --ink: #e9edf7;
  --ink-soft: rgba(233, 237, 247, 0.62);
  --ink-faint: rgba(233, 237, 247, 0.38);
  --rule: rgba(132, 160, 220, 0.18);
  --green: #7bd389;
  --blue: #58c4dd;
  --orange: #f5c857;
  --pink: #e07a9e;
  --red: #fc6255;
  --gold: #f5c857;
  --display: 'STIX Two Text', Georgia, serif;
  --body: 'Atkinson Hyperlegible', sans-serif;
  --mono: 'IBM Plex Mono', monospace;
  --radius: 10px;
  --card-shadow: 0 0 0 1px rgba(132, 160, 220, 0.13), 0 14px 50px rgba(0, 0, 0, 0.5);
}

* { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--body);
  font-size: 17px;
  line-height: 1.6;
  color: var(--ink);
  background-color: var(--paper);
  background-image:
    radial-gradient(1100px 700px at 85% -120px, rgba(88, 196, 221, 0.09), transparent 65%),
    radial-gradient(1000px 800px at 8% 35%, rgba(140, 100, 230, 0.07), transparent 65%),
    radial-gradient(900px 700px at 90% 85%, rgba(252, 98, 85, 0.05), transparent 65%),
    linear-gradient(rgba(132, 170, 235, 0.065) 1px, transparent 1px),
    linear-gradient(90deg, rgba(132, 170, 235, 0.065) 1px, transparent 1px);
  background-size: 100% 100%, 100% 100%, 100% 100%, 44px 44px, 44px 44px;
  background-attachment: fixed;
  overflow-x: hidden;
}

h1, h2, h3 {
  font-family: var(--display);
  font-weight: 600;
  line-height: 1.12;
}

p { margin: 0; }

a { color: var(--blue); }

::selection { background: rgba(88, 196, 221, 0.3); }

.eyebrow {
  font: 600 12.5px var(--mono);
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--c, var(--ink-faint));
}

.lede {
  font-size: 18.5px;
  color: var(--ink-soft);
}

.lede strong { color: var(--ink); }

.c-green { color: var(--green); }
.c-blue { color: var(--blue); }
.c-orange { color: var(--orange); }
.c-pink { color: var(--pink); }
.c-red { color: var(--red); }

/* Clickable terms that open a deep-dive popup */
.term {
  border: none;
  background: none;
  font: inherit;
  font-weight: 700;
  color: var(--blue);
  border-bottom: 2px dotted var(--blue);
  cursor: help;
  padding: 0;
}

/* Callouts */
.callout {
  background: rgba(132, 160, 220, 0.06);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  padding: 18px 22px;
  margin: 28px auto 0;
  max-width: 720px;
  font-size: 16.5px;
  color: var(--ink-soft);
}

.callout strong, .callout em { color: var(--ink); }

.callout-label {
  font: 700 11px var(--mono);
  letter-spacing: 0.14em;
  text-transform: uppercase;
  display: block;
  margin-bottom: 6px;
}

.callout.insight {
  border-color: rgba(123, 211, 137, 0.35);
  background: rgba(123, 211, 137, 0.07);
}
.callout.insight .callout-label { color: var(--green); }

.callout.gotcha {
  background: rgba(245, 200, 87, 0.08);
  border: none;
  border-left: 3px solid var(--orange);
  border-radius: 6px;
}
.callout.gotcha .callout-label { color: var(--orange); }

.callout.note {
  font-size: 15.5px;
}
.callout.note .callout-label { color: var(--ink-faint); }

/* Stacked fractions, usable in prose and in the equation displays */
.frac {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  vertical-align: middle;
  line-height: 1.15;
  margin: 0 2px;
}
.frac .num, .frac .den { font-size: 0.78em; padding: 0 4px; }
.frac .den { border-top: 1.5px solid currentColor; }