/* ============================================================================
   The Field Guide to AI Memory — design system
   Direction: "engineering field notes / technical archive."
   Display serif (Fraunces) + reading serif (Source Serif 4) + mono chrome
   (JetBrains Mono). Warm paper light / deep ink dark. One disciplined amber accent.
   ============================================================================ */

:root {
  --font-display: 'Fraunces', Georgia, 'Times New Roman', serif;
  --font-body: 'Source Serif 4', Georgia, serif;
  --font-mono: 'JetBrains Mono', ui-monospace, 'SF Mono', Menlo, monospace;

  --measure: 44rem;
  --sidebar-w: 19rem;
  --rail-w: 15rem;
  --topbar-h: 3.75rem;
  --radius: 4px;
  --radius-lg: 8px;
  --ease: cubic-bezier(0.22, 0.61, 0.36, 1);
}

/* ---- dark (default): deep ink ---- */
:root, [data-theme="dark"] {
  --bg: #15151a;
  --bg-soft: #1b1b21;
  --bg-code: #1a1a20;
  --surface: #1d1d24;
  --line: #2c2c35;
  --line-soft: #24242c;
  --ink: #ece6d8;
  --ink-soft: #b9b4a8;
  --ink-faint: #837e74;
  --accent: #e0a23e;       /* amber — recall / highlighter */
  --accent-strong: #f0b657;
  --accent-tint: rgba(224, 162, 62, 0.13);
  --link: #d8a14a;
  --teal: #5fc7bd;
  --grain-opacity: 0.035;
  --shadow: 0 18px 50px -22px rgba(0, 0, 0, 0.7);
  color-scheme: dark;
}

/* ---- light: warm paper ---- */
[data-theme="light"] {
  --bg: #f7f3ea;
  --bg-soft: #f1ece0;
  --bg-code: #fbf8f1;
  --surface: #fffdf8;
  --line: #e2dac9;
  --line-soft: #ece5d6;
  --ink: #211f1a;
  --ink-soft: #5a554a;
  --ink-faint: #8c8678;
  --accent: #b3701a;
  --accent-strong: #97600f;
  --accent-tint: rgba(179, 112, 26, 0.10);
  --link: #9a5d12;
  --teal: #1d7d72;
  --grain-opacity: 0.04;
  --shadow: 0 18px 50px -24px rgba(70, 55, 20, 0.28);
  color-scheme: light;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: calc(var(--topbar-h) + 1.25rem); }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } * { animation: none !important; transition: none !important; } }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 1.0625rem;
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  font-optical-sizing: auto;
}

/* faint paper grain for atmosphere */
body::before {
  content: ""; position: fixed; inset: 0; z-index: 0; pointer-events: none;
  opacity: var(--grain-opacity);
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='160' height='160'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}

a { color: var(--link); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 2px; }
.ext { font-size: 0.72em; color: var(--ink-faint); margin-left: 1px; vertical-align: 0.18em; }

/* ---------- progress ---------- */
.progress { position: fixed; top: 0; left: 0; height: 2px; width: 0; background: linear-gradient(90deg, var(--accent), var(--accent-strong)); z-index: 60; transition: width 0.1s linear; }

/* ---------- topbar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 50; height: var(--topbar-h);
  display: flex; align-items: center; gap: 0.75rem; padding: 0 1.1rem;
  background: color-mix(in srgb, var(--bg) 84%, transparent);
  backdrop-filter: saturate(1.4) blur(10px);
  border-bottom: 1px solid var(--line);
}
.topbar__spacer { flex: 1; }
.brand { display: flex; align-items: center; gap: 0.55rem; }
.brand:hover { text-decoration: none; }
.brand__mark { width: 17px; height: 17px; border-radius: 3px; background: var(--accent); box-shadow: 0 0 0 3px var(--accent-tint); position: relative; }
.brand__mark::after { content: ""; position: absolute; inset: 5px 5px auto auto; width: 4px; height: 4px; border-radius: 50%; background: var(--bg); }
.brand__text { font-family: var(--font-mono); font-weight: 600; font-size: 0.82rem; letter-spacing: 0.06em; text-transform: uppercase; color: var(--ink); }

.icon-btn { background: none; border: 1px solid transparent; color: var(--ink-soft); cursor: pointer; width: 2.1rem; height: 2.1rem; border-radius: var(--radius); display: inline-flex; align-items: center; justify-content: center; font-size: 1.05rem; }
.icon-btn:hover { background: var(--bg-soft); color: var(--ink); }
.menu-toggle { display: none; }

.theme-toggle__icon { width: 15px; height: 15px; border-radius: 50%; background: var(--ink-soft); box-shadow: inset -4px -4px 0 0 var(--bg); transition: all 0.3s var(--ease); }
[data-theme="light"] .theme-toggle__icon { background: var(--accent); box-shadow: 0 0 0 2px var(--accent-tint); }

.search-trigger { display: flex; align-items: center; gap: 0.6rem; background: var(--bg-soft); border: 1px solid var(--line); color: var(--ink-faint); border-radius: var(--radius); padding: 0.4rem 0.7rem; cursor: pointer; font-family: var(--font-mono); font-size: 0.76rem; }
.search-trigger:hover { border-color: var(--accent); color: var(--ink-soft); }
.search-trigger kbd, .search-hint kbd { font-family: var(--font-mono); font-size: 0.68rem; background: var(--surface); border: 1px solid var(--line); border-radius: 3px; padding: 0.05rem 0.32rem; color: var(--ink-soft); }

/* ---------- layout ---------- */
.layout { position: relative; z-index: 1; display: grid; grid-template-columns: var(--sidebar-w) minmax(0, 1fr); max-width: 92rem; margin: 0 auto; }

.sidebar { border-right: 1px solid var(--line); }
.sidebar__inner { position: sticky; top: var(--topbar-h); max-height: calc(100vh - var(--topbar-h)); overflow-y: auto; padding: 1.6rem 1.1rem 4rem 1.5rem; scrollbar-width: thin; }
.sidebar__title { display: block; font-family: var(--font-display); font-weight: 600; font-size: 1.02rem; line-height: 1.25; color: var(--ink); margin-bottom: 1.5rem; }
.sidebar__title:hover { text-decoration: none; color: var(--accent); }

.nav-group { margin-bottom: 1.4rem; }
.nav-group__label { font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.1em; text-transform: uppercase; color: var(--ink-faint); margin: 0 0 0.55rem; }
.nav-group ul { list-style: none; margin: 0; padding: 0; }
.nav-link { display: block; padding: 0.27rem 0.7rem; margin-left: -0.7rem; border-radius: var(--radius); font-size: 0.95rem; color: var(--ink-soft); line-height: 1.4; border-left: 2px solid transparent; }
.nav-link:hover { color: var(--ink); background: var(--bg-soft); text-decoration: none; }
.nav-link.is-active { color: var(--accent); background: var(--accent-tint); border-left-color: var(--accent); font-weight: 600; }

.scrim { display: none; }

/* ---------- content ---------- */
.content { display: grid; grid-template-columns: minmax(0, 1fr) var(--rail-w); gap: 2.5rem; padding: 2.6rem clamp(1.25rem, 4vw, 4rem) 5rem; }
.doc { min-width: 0; max-width: var(--measure); }
.doc__eyebrow { font-family: var(--font-mono); font-size: 0.72rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--accent); margin-bottom: 1rem; }
.doc__eyebrow .reading { color: var(--ink-faint); }
.doc__title { font-family: var(--font-display); font-weight: 600; font-size: clamp(2.1rem, 4.5vw, 3rem); line-height: 1.08; letter-spacing: -0.012em; margin: 0 0 1rem; }
.doc__lede { font-size: 1.27rem; line-height: 1.55; color: var(--ink-soft); font-style: italic; margin: 0 0 2.2rem; padding-bottom: 1.6rem; border-bottom: 1px solid var(--line); }

/* prose */
.doc__body { font-size: 1.0625rem; }
.doc__body > *:first-child { margin-top: 0; }
.doc__body p { margin: 0 0 1.25rem; }
.doc__body h2 { font-family: var(--font-display); font-weight: 600; font-size: 1.72rem; line-height: 1.2; letter-spacing: -0.01em; margin: 2.9rem 0 1rem; padding-top: 0.4rem; }
.doc__body h3 { font-family: var(--font-display); font-weight: 600; font-size: 1.3rem; margin: 2.1rem 0 0.8rem; }
.doc__body h4 { font-family: var(--font-mono); font-weight: 600; font-size: 0.92rem; letter-spacing: 0.02em; text-transform: uppercase; color: var(--ink-soft); margin: 1.8rem 0 0.6rem; }
.h-anchor { position: relative; }
.h-anchor .anchor { position: absolute; left: -1.4rem; color: var(--ink-faint); opacity: 0; font-family: var(--font-mono); text-decoration: none; font-weight: 400; }
.h-anchor:hover .anchor { opacity: 1; }
.h-anchor .anchor:hover { color: var(--accent); }

.doc__body ul, .doc__body ol { margin: 0 0 1.3rem; padding-left: 1.4rem; }
.doc__body li { margin: 0.35rem 0; padding-left: 0.25rem; }
.doc__body li::marker { color: var(--accent); }
.doc__body strong { font-weight: 600; color: var(--ink); }
.doc__body em { font-style: italic; }
.doc__body hr { border: none; border-top: 1px solid var(--line); margin: 2.6rem 0; }

/* inline code */
.doc__body :not(pre) > code { font-family: var(--font-mono); font-size: 0.84em; background: var(--bg-soft); border: 1px solid var(--line-soft); border-radius: 3px; padding: 0.1em 0.36em; color: var(--ink); word-break: break-word; }

/* blockquote */
.doc__body blockquote { margin: 1.6rem 0; padding: 0.2rem 0 0.2rem 1.3rem; border-left: 3px solid var(--line); color: var(--ink-soft); font-style: italic; }
.doc__body blockquote p:last-child { margin-bottom: 0; }

/* code blocks */
.code-block { position: relative; margin: 1.6rem 0; border: 1px solid var(--line); border-radius: var(--radius-lg); overflow: hidden; background: var(--bg-code); }
.code-block::before { content: attr(data-lang); position: absolute; top: 0; left: 0; font-family: var(--font-mono); font-size: 0.64rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--ink-faint); padding: 0.4rem 0.7rem; }
.code-block pre.shiki { margin: 0; padding: 2rem 1.1rem 1.1rem; overflow-x: auto; font-size: 0.85rem; line-height: 1.6; background: transparent !important; }
.code-block pre.shiki code { font-family: var(--font-mono); }
.code-copy { position: absolute; top: 0.45rem; right: 0.5rem; z-index: 2; font-family: var(--font-mono); font-size: 0.66rem; text-transform: uppercase; letter-spacing: 0.05em; background: var(--surface); border: 1px solid var(--line); color: var(--ink-soft); border-radius: 3px; padding: 0.2rem 0.5rem; cursor: pointer; opacity: 0; transition: opacity 0.15s; }
.code-block:hover .code-copy { opacity: 1; }
.code-copy:hover { color: var(--accent); border-color: var(--accent); }
.code-copy.copied { color: var(--teal); border-color: var(--teal); }

/* shiki dual theme */
.shiki, .shiki span { color: var(--shiki-light); }
[data-theme="dark"] .shiki, [data-theme="dark"] .shiki span { color: var(--shiki-dark); }

/* figures */
.figure { margin: 1.9rem 0; text-align: center; }
.figure img { max-width: 100%; height: auto; border-radius: var(--radius-lg); border: 1px solid var(--line); background: var(--surface); }
.figure svg { max-width: 100%; height: auto; }
.figure figcaption { font-family: var(--font-mono); font-size: 0.74rem; color: var(--ink-faint); margin-top: 0.7rem; line-height: 1.5; }

/* tables */
.doc__body table { width: 100%; border-collapse: collapse; margin: 1.7rem 0; font-size: 0.92rem; }
.doc__body th, .doc__body td { text-align: left; padding: 0.6rem 0.85rem; border-bottom: 1px solid var(--line); vertical-align: top; }
.doc__body thead th { font-family: var(--font-mono); font-size: 0.72rem; letter-spacing: 0.05em; text-transform: uppercase; color: var(--ink-soft); border-bottom: 2px solid var(--line); }
.doc__body tbody tr:hover { background: var(--bg-soft); }

/* callouts */
.callout { margin: 1.7rem 0; padding: 1rem 1.2rem; border-radius: var(--radius-lg); border: 1px solid var(--line); border-left: 3px solid var(--ink-faint); background: var(--bg-soft); }
.callout__label { font-family: var(--font-mono); font-size: 0.7rem; letter-spacing: 0.08em; text-transform: uppercase; margin: 0 0 0.45rem; color: var(--ink-soft); }
.callout__body > *:last-child { margin-bottom: 0; }
.callout__body p { margin-bottom: 0.7rem; }
.callout--key { border-left-color: var(--accent); background: var(--accent-tint); }
.callout--key .callout__label { color: var(--accent-strong); }
.callout--tip { border-left-color: var(--teal); }
.callout--tip .callout__label { color: var(--teal); }
.callout--warning { border-left-color: #d9803a; }
.callout--warning .callout__label { color: #d9803a; }
.callout--story { border-left-color: var(--teal); background: color-mix(in srgb, var(--teal) 7%, transparent); }
.callout--story .callout__label { color: var(--teal); }
.callout--cite { font-size: 0.9rem; }

/* footer / pager / cite */
.doc__footer { margin-top: 3.5rem; padding-top: 1.8rem; border-top: 1px solid var(--line); }
.citebox { margin-bottom: 2rem; }
.citebox summary { font-family: var(--font-mono); font-size: 0.72rem; letter-spacing: 0.06em; text-transform: uppercase; color: var(--ink-faint); cursor: pointer; }
.citebox summary:hover { color: var(--accent); }
.citebox__text { margin: 0.7rem 0 0; font-size: 0.9rem; color: var(--ink-soft); background: var(--bg-soft); border: 1px solid var(--line); border-radius: var(--radius); padding: 0.8rem 1rem; }
.pager { display: flex; justify-content: space-between; gap: 1rem; }
.pager__link { display: flex; flex-direction: column; gap: 0.2rem; padding: 0.9rem 1.1rem; border: 1px solid var(--line); border-radius: var(--radius-lg); flex: 1; max-width: 49%; transition: border-color 0.15s; }
.pager__link:hover { border-color: var(--accent); text-decoration: none; }
.pager__next { text-align: right; align-items: flex-end; }
.pager__dir { font-family: var(--font-mono); font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.05em; color: var(--ink-faint); }
.pager__title { font-family: var(--font-display); font-size: 1.02rem; color: var(--ink); font-weight: 500; }

/* on-this-page rail */
.rail { position: relative; }
.toc { position: sticky; top: calc(var(--topbar-h) + 1.6rem); max-height: calc(100vh - var(--topbar-h) - 3rem); overflow-y: auto; }
.toc__label { font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.1em; text-transform: uppercase; color: var(--ink-faint); margin: 0 0 0.7rem; }
.toc ul { list-style: none; margin: 0; padding: 0; border-left: 1px solid var(--line); }
.toc__item a { display: block; padding: 0.22rem 0 0.22rem 0.9rem; margin-left: -1px; border-left: 2px solid transparent; font-size: 0.85rem; color: var(--ink-faint); line-height: 1.4; }
.toc__item--h3 a { padding-left: 1.7rem; font-size: 0.82rem; }
.toc__item a:hover { color: var(--ink); text-decoration: none; }
.toc__item a.is-active { color: var(--accent); border-left-color: var(--accent); }

/* search modal */
.search-modal { position: fixed; inset: 0; z-index: 80; background: color-mix(in srgb, var(--bg) 60%, rgba(0,0,0,0.5)); display: flex; align-items: flex-start; justify-content: center; padding-top: 12vh; }
.search-modal[hidden] { display: none; }
.search-modal__panel { width: min(38rem, 92vw); background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius-lg); box-shadow: var(--shadow); padding: 0.9rem; }
#searchInput { width: 100%; background: var(--bg); border: 1px solid var(--line); border-radius: var(--radius); padding: 0.7rem 0.9rem; color: var(--ink); font-family: var(--font-body); font-size: 1.05rem; outline: none; }
#searchInput:focus { border-color: var(--accent); }
.search-results { list-style: none; margin: 0.7rem 0 0; padding: 0; max-height: 52vh; overflow-y: auto; }
.search-results li a { display: block; padding: 0.6rem 0.7rem; border-radius: var(--radius); color: var(--ink); }
.search-results li a:hover, .search-results li a.is-active { background: var(--accent-tint); text-decoration: none; }
.search-results .sr-title { font-family: var(--font-display); font-weight: 500; }
.search-results .sr-part { font-family: var(--font-mono); font-size: 0.68rem; text-transform: uppercase; letter-spacing: 0.05em; color: var(--ink-faint); }
.search-results .sr-snippet { font-size: 0.85rem; color: var(--ink-soft); margin-top: 0.15rem; }
.search-results mark { background: var(--accent-tint); color: var(--accent-strong); padding: 0 1px; border-radius: 2px; }
.search-hint { font-family: var(--font-mono); font-size: 0.68rem; color: var(--ink-faint); margin: 0.7rem 0 0.2rem; display: flex; gap: 0.4rem; align-items: center; }

/* ---------- responsive ---------- */
@media (max-width: 1100px) {
  .content { grid-template-columns: minmax(0, 1fr); }
  .rail { display: none; }
}
@media (max-width: 820px) {
  .menu-toggle { display: inline-flex; }
  .layout { grid-template-columns: minmax(0, 1fr); }
  .sidebar { position: fixed; top: var(--topbar-h); bottom: 0; left: 0; width: min(20rem, 84vw); background: var(--bg); z-index: 45; transform: translateX(-105%); transition: transform 0.28s var(--ease); border-right: 1px solid var(--line); }
  .sidebar.is-open { transform: translateX(0); box-shadow: var(--shadow); }
  .sidebar__inner { height: 100%; max-height: none; }
  .scrim.is-open { display: block; position: fixed; inset: var(--topbar-h) 0 0; background: rgba(0,0,0,0.4); z-index: 44; }
  .search-trigger span { display: none; }
}

::selection { background: var(--accent-tint); }