/* Palette taken from the book cover: navy, teal, and umber bands with gold signal lines. */
:root {
  color-scheme: dark;
  --navy: #121f3d;
  --navy-2: #182a4f;
  --teal: #1c4548;
  --umber: #2a221f;
  --ink: #e9ecf2;
  --muted: #a8b1c3;
  --faint: #76819a;
  --rule: #2c3b5e;
  --gold: #e9b24a;
  --gold-soft: rgba(233, 178, 74, .14);
  --green: #62b98a;
  --rust: #d8643f;
  --surface: #172745;
  --serif: "Source Serif 4", Georgia, serif;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --mono: "IBM Plex Mono", ui-monospace, Menlo, monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 64px; }
body { margin: 0; background: var(--navy); color: var(--ink); font: 16px/1.65 var(--sans); -webkit-font-smoothing: antialiased; }
a { color: var(--gold); text-decoration: none; }
a:hover { text-decoration: underline; }
h1, h2, h3 { font-family: var(--serif); line-height: 1.2; margin: 0; }
h2 { font-size: clamp(1.6rem, 3.2vw, 2.2rem); font-weight: 600; }
h3 { font-size: 1.12rem; font-weight: 600; }
p { margin: 0 0 1rem; }
.wrap { max-width: 1080px; margin: 0 auto; padding: 0 16px; }
.label { font: 500 .72rem var(--mono); letter-spacing: .1em; text-transform: uppercase; color: var(--faint); }
.label b { color: var(--gold); font-weight: 500; }

/* Circuit grid background */
.grid-bg {
  background-image:
    linear-gradient(rgba(255,255,255,.035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,.035) 1px, transparent 1px);
  background-size: 36px 36px;
}

.nav { position: sticky; top: 0; z-index: 10; background: rgba(18, 31, 61, .9); backdrop-filter: blur(8px); border-bottom: 1px solid var(--rule); }
.nav .wrap { display: flex; align-items: center; gap: 1.25rem; padding-top: .7rem; padding-bottom: .7rem; flex-wrap: wrap; }
.brand { font: 700 1.1rem var(--serif); color: var(--ink); }
.brand span { color: var(--gold); }
.nav .links { display: flex; gap: 1rem; flex-wrap: wrap; margin-left: auto; font-size: .9rem; }
.nav .links a { color: var(--muted); }
.nav .links a:hover { color: var(--ink); text-decoration: none; }

section { padding: 4rem 0; }
.band-teal { background: var(--teal); }
.band-umber { background: var(--umber); }
.band-navy2 { background: var(--navy-2); }
.sec-head { margin-bottom: 2rem; max-width: 70ch; }
.sec-head .label { display: block; margin-bottom: .6rem; }
.sec-head p { color: var(--muted); margin-top: .8rem; }

/* Hero */
.hero { padding: 4rem 0; border-bottom: 1px solid var(--rule); }
.hero .grid { display: grid; grid-template-columns: 1fr 300px; gap: 3rem; align-items: center; }
.hero h1 { font-size: clamp(3rem, 8vw, 5.2rem); font-weight: 700; letter-spacing: -.02em; }
.hero h1 span { color: var(--gold); }
.hero .sub { font: 400 clamp(1.1rem, 2.3vw, 1.4rem) var(--serif); color: var(--ink); margin: .6rem 0 .3rem; }
.hero .by { color: var(--muted); margin-bottom: 1.5rem; }
.hero .lede { max-width: 60ch; color: var(--ink); }
.hero .cover img { width: 100%; height: auto; display: block; border-radius: 3px; box-shadow: 0 16px 40px rgba(0,0,0,.45); }
.btns { display: flex; flex-wrap: wrap; gap: .6rem; }
.btn { display: inline-block; padding: .55rem 1rem; border: 1.5px solid var(--gold); color: var(--gold); font-size: .92rem; font-weight: 500; border-radius: 4px; }
.btn:hover { background: var(--gold-soft); text-decoration: none; }
.btn.primary { background: var(--gold); color: var(--navy); }
.btn.primary:hover { background: #f3c468; }
.facts { display: flex; gap: 2rem; flex-wrap: wrap; margin-top: 2rem; }
.facts b { display: block; font: 600 1.5rem var(--serif); color: var(--gold); }
.facts span { font-size: .8rem; color: var(--muted); }

/* Answer vs act */
.systems { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; }
.sys { background: rgba(0,0,0,.18); border: 1px solid rgba(255,255,255,.1); border-radius: 6px; padding: 1.2rem 1.3rem; }
.sys .tag { font: 600 .8rem var(--mono); color: var(--navy); background: var(--muted); padding: .1rem .45rem; border-radius: 3px; }
.sys.act .tag { background: var(--gold); }
.sys h3 { margin: .7rem 0 .4rem; }
.sys p { color: var(--muted); font-size: .94rem; margin: 0 0 .6rem; }
.sys .err { font-size: .85rem; color: var(--ink); border-top: 1px dashed rgba(255,255,255,.15); padding-top: .6rem; margin: 0; }
.sys .err b { color: var(--rust); font-weight: 600; }
.pull { margin-top: 1.6rem; font: italic 1.15rem var(--serif); max-width: 62ch; border-left: 3px solid var(--gold); padding-left: 1rem; }

/* Questions */
.qs { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1px; background: var(--rule); border: 1px solid var(--rule); }
.q { background: var(--navy); padding: 1.3rem 1.3rem 1.4rem; }
.q .n { font: 500 .78rem var(--mono); color: var(--gold); }
.q h3 { margin: .35rem 0 .45rem; }
.q p { color: var(--muted); font-size: .93rem; margin: 0; }

/* Parts */
.parts { display: grid; grid-template-columns: repeat(3, 1fr); gap: 0; border-radius: 6px; overflow: hidden; }
.part { padding: 1.5rem 1.4rem; }
.part:nth-child(1) { background: var(--navy-2); }
.part:nth-child(2) { background: var(--teal); }
.part:nth-child(3) { background: var(--umber); }
.part .label { color: var(--gold); }
.part h3 { font-size: 1.3rem; margin: .4rem 0 .6rem; }
.part p { color: var(--muted); font-size: .94rem; }
.part ul { margin: 0; padding-left: 1.1rem; font-size: .9rem; }
.part li { margin: .15rem 0; }
.thesis { margin-top: 1.5rem; display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; font-size: .95rem; }
.thesis div { border-top: 2px solid var(--gold); padding-top: .6rem; color: var(--muted); }
.thesis b { color: var(--ink); }

/* Reliability lab */
.lab { display: grid; grid-template-columns: 330px 1fr; gap: 2rem; background: rgba(0,0,0,.2); border: 1px solid rgba(255,255,255,.12); border-radius: 8px; padding: 1.5rem; }
.presets { display: flex; flex-wrap: wrap; gap: .4rem; margin-bottom: 1.1rem; }
.presets button { font: 500 .8rem var(--sans); color: var(--ink); background: transparent; border: 1px solid var(--rule); border-radius: 999px; padding: .3rem .75rem; cursor: pointer; }
.presets button:hover { border-color: var(--gold); }
.presets button[aria-pressed="true"] { background: var(--gold); border-color: var(--gold); color: var(--navy); }
.field { margin-bottom: .9rem; }
.field label { display: flex; justify-content: space-between; gap: .5rem; font-size: .87rem; margin-bottom: .2rem; }
.field label span i { font-family: var(--serif); color: var(--gold); font-size: 1rem; }
.field output { font-family: var(--mono); color: var(--gold); }
.field input { width: 100%; accent-color: var(--gold); }
.field small { display: block; font-size: .76rem; color: var(--faint); margin-top: .1rem; }
.readout { display: grid; grid-template-columns: repeat(4, 1fr); gap: .75rem; margin-bottom: 1rem; }
.readout div { border-top: 3px solid var(--rule); padding-top: .4rem; }
.readout .g { border-top-color: var(--green); }
.readout .e { border-top-color: var(--gold); }
.readout .f { border-top-color: var(--rust); }
.readout b { display: block; font: 600 1.4rem var(--serif); font-variant-numeric: tabular-nums; }
.readout span { font-size: .78rem; color: var(--muted); }
.subread { font-size: .88rem; color: var(--muted); margin-bottom: .5rem; }
.subread b { color: var(--ink); font-family: var(--mono); font-weight: 500; }
#rel-chart { width: 100%; height: auto; display: block; }
#rel-chart text { font: 13px var(--mono); fill: var(--faint); }
#rel-chart .axis { stroke: rgba(255,255,255,.08); }
.legend { display: flex; gap: 1.2rem; flex-wrap: wrap; font-size: .8rem; color: var(--muted); margin-top: .4rem; }
.legend i { display: inline-block; width: 12px; height: 12px; border-radius: 2px; vertical-align: -1px; margin-right: .35rem; }
.chain-note { font-size: .82rem; color: var(--faint); margin-top: .9rem; }
.formula { font-family: var(--mono); font-size: .85rem; background: var(--gold-soft); color: var(--ink); padding: .55rem .8rem; border-radius: 4px; margin-top: .8rem; overflow-x: auto; white-space: nowrap; }

.lab > * { min-width: 0; }

/* Examples */
.examples { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; }
.ex { background: var(--surface); border: 1px solid var(--rule); border-radius: 6px; padding: 1.3rem; }
.ex .tag { font: 600 .9rem var(--mono); color: var(--navy); background: var(--gold); padding: .1rem .45rem; border-radius: 3px; }
.ex h3 { margin: .7rem 0 .4rem; }
.ex p { color: var(--muted); font-size: .93rem; margin: 0 0 .6rem; }
.ex .stress { font-size: .85rem; color: var(--ink); margin: 0; }
.ex .stress b { color: var(--gold); font-weight: 500; font-family: var(--mono); font-size: .75rem; text-transform: uppercase; letter-spacing: .06em; display: block; margin-bottom: .15rem; }

/* Courses & labs */
.two { display: grid; grid-template-columns: 1fr 1fr; gap: 2.5rem; }
.course { border-left: 3px solid var(--gold); padding: .2rem 0 .2rem 1rem; margin-bottom: 1.1rem; }
.course h3 { font-size: 1.05rem; }
.course p { color: var(--muted); font-size: .92rem; margin: .2rem 0 0; }
.labs { list-style: none; margin: 0; padding: 0; counter-reset: lab; }
.labs li { display: flex; gap: .9rem; align-items: baseline; padding: .55rem 0; border-bottom: 1px dashed var(--rule); }
.labs li::before { counter-increment: lab; content: "Lab " counter(lab); font: 500 .78rem var(--mono); color: var(--gold); min-width: 3.4rem; }

/* Contents */
.toc { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1.5rem; }
.toc h3 { font-size: 1rem; color: var(--gold); margin-bottom: .6rem; }
.toc h3 span { display: block; font: 500 .72rem var(--mono); color: var(--faint); letter-spacing: .08em; text-transform: uppercase; margin-bottom: .15rem; }
.toc ol { list-style: none; margin: 0; padding: 0; font-size: .93rem; }
.toc li { display: flex; gap: .6rem; padding: .28rem 0; border-bottom: 1px solid rgba(255,255,255,.06); }
.toc li .c { font: .8rem var(--mono); color: var(--faint); min-width: 1.4rem; padding-top: .1rem; }
.toc .in-sample { font: .7rem var(--mono); color: var(--green); margin-left: .35rem; white-space: nowrap; }

/* Papers */
.papers { list-style: none; margin: 0; padding: 0; columns: 2; column-gap: 2.5rem; }
.papers li { break-inside: avoid; padding: .75rem 0; border-bottom: 1px dashed var(--rule); }
.papers .t { font: 600 1rem var(--serif); }
.papers .m { color: var(--muted); font-size: .88rem; }
.see { margin-top: 1.8rem; display: flex; gap: .8rem; flex-wrap: wrap; }

footer { padding: 2rem 0 3rem; color: var(--faint); font-size: .85rem; border-top: 1px solid var(--rule); }
footer .wrap { display: flex; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }

@media (max-width: 880px) {
  .hero .grid, .lab, .two { grid-template-columns: 1fr; }
  .hero .cover { max-width: 240px; }
  .systems, .qs, .parts, .thesis, .examples, .toc { grid-template-columns: 1fr; }
  .readout { grid-template-columns: 1fr 1fr; }
  .papers { columns: 1; }
  .lab { padding: 1.1rem; }
  section { padding: 3rem 0; }
}
@media (max-width: 520px) { .nav .links { margin-left: 0; gap: .8rem; } }