:root {
  --bg: #fbfaf7;
  --surface: #ffffff;
  --surface-2: #f3f1ec;
  --text: #1d2126;
  --muted: #5d6670;
  --faint: #8a929b;
  --line: #e4e0d8;
  --accent: #326891;
  --accent-soft: #e6eef5;
  --accent-text: #26557a;
  --good: #2f7d4f;
  --good-soft: #e5f2ea;
  --warn: #9a5b0f;
  --warn-soft: #f8eedf;
  --bad: #a13d3d;
  --bad-soft: #f7e6e6;
  --week-past: #326891;
  --week-future: #dcd8cf;
  --week-now: #d9822b;
  --serif: "Source Serif 4", Georgia, serif;
  --sans: "Inter", system-ui, -apple-system, "Segoe UI", sans-serif;
  --sidebar: 290px;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #14171a; --surface: #1b1f23; --surface-2: #22272c; --text: #e6e3dd; --muted: #a3abb3; --faint: #78818a;
    --line: #2f353b; --accent: #7fb0d6; --accent-soft: #1d2d3a; --accent-text: #9cc4e3;
    --good: #7cc79a; --good-soft: #1b2e23; --warn: #e0b060; --warn-soft: #33291a; --bad: #e38c8c; --bad-soft: #352020;
    --week-past: #5d93bd; --week-future: #2c3238; --week-now: #e39a4f; color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #14171a; --surface: #1b1f23; --surface-2: #22272c; --text: #e6e3dd; --muted: #a3abb3; --faint: #78818a;
  --line: #2f353b; --accent: #7fb0d6; --accent-soft: #1d2d3a; --accent-text: #9cc4e3;
  --good: #7cc79a; --good-soft: #1b2e23; --warn: #e0b060; --warn-soft: #33291a; --bad: #e38c8c; --bad-soft: #352020;
  --week-past: #5d93bd; --week-future: #2c3238; --week-now: #e39a4f; color-scheme: dark;
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: 72px; }
body { margin: 0; background: var(--bg); color: var(--text); font: 17px/1.65 var(--serif); }
a { color: var(--accent-text); text-underline-offset: 3px; text-decoration-thickness: 1px; }
a:hover { text-decoration-thickness: 2px; }

/* Top bar */
.topbar {
  position: sticky; top: 0; z-index: 30; height: 56px; display: flex; align-items: center; gap: 12px;
  padding: 0 16px; background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(10px); -webkit-backdrop-filter: blur(10px); border-bottom: 1px solid var(--line);
  font-family: var(--sans);
}
.brand { font-weight: 700; font-size: 15px; color: var(--text); text-decoration: none; display: flex; align-items: center; gap: 9px; letter-spacing: -.01em; }
.brand-mark { width: 18px; height: 18px; border-radius: 4px; background:
  linear-gradient(var(--accent) 0 0) 0 0/5px 5px no-repeat, linear-gradient(var(--accent) 0 0) 6.5px 0/5px 5px no-repeat,
  linear-gradient(var(--accent) 0 0) 13px 0/5px 5px no-repeat, linear-gradient(var(--accent) 0 0) 0 6.5px/5px 5px no-repeat,
  linear-gradient(var(--accent) 0 0) 6.5px 6.5px/5px 5px no-repeat, linear-gradient(var(--line) 0 0) 13px 6.5px/5px 5px no-repeat,
  linear-gradient(var(--line) 0 0) 0 13px/5px 5px no-repeat, linear-gradient(var(--line) 0 0) 6.5px 13px/5px 5px no-repeat,
  linear-gradient(var(--line) 0 0) 13px 13px/5px 5px no-repeat; }
.theme-btn, .menu-btn { margin-left: auto; width: 36px; height: 36px; display: grid; place-items: center; border: 1px solid var(--line);
  border-radius: 8px; background: var(--surface); color: var(--muted); cursor: pointer; }
.menu-btn { margin-left: 0; display: none; }
.theme-btn:hover, .menu-btn:hover { color: var(--text); }
.i-moon { display: none; }
:root[data-theme="dark"] .i-sun { display: none; }
:root[data-theme="dark"] .i-moon { display: block; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .i-sun { display: none; } :root:not([data-theme="light"]) .i-moon { display: block; } }
.progress { position: fixed; top: 0; left: 0; right: 0; height: 3px; z-index: 40; }
.progress span { display: block; height: 100%; width: 0; background: var(--accent); }

/* Layout */
.layout { display: grid; grid-template-columns: var(--sidebar) minmax(0, 1fr); }
.sidebar { position: sticky; top: 56px; height: calc(100vh - 56px); overflow-y: auto; padding: 20px 16px 40px 20px;
  border-right: 1px solid var(--line); font-family: var(--sans); font-size: 14px; }
.nav-home { display: block; font-weight: 600; color: var(--text); text-decoration: none; padding: 6px 8px; border-radius: 6px; }
.nav-home:hover { background: var(--surface-2); }
.nav-part { margin: 20px 8px 6px; font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: .07em; color: var(--faint); }
.nav-list { list-style: none; margin: 0; padding: 0; }
.nav-list a { display: flex; gap: 10px; padding: 6px 8px; border-radius: 6px; color: var(--muted); text-decoration: none; line-height: 1.4; }
.nav-list a:hover { background: var(--surface-2); color: var(--text); }
.nav-list a[aria-current="page"] { background: var(--accent-soft); color: var(--accent-text); font-weight: 600; }
.nav-num { font-variant-numeric: tabular-nums; color: var(--faint); font-size: 12px; padding-top: 1px; }
.nav-list a[aria-current="page"] .nav-num { color: inherit; }
.main { min-width: 0; padding: 48px 24px 40px; }
.scrim { display: none; }

@media (max-width: 960px) {
  .layout { grid-template-columns: 1fr; }
  .menu-btn { display: grid; }
  .sidebar { position: fixed; top: 56px; left: 0; bottom: 0; height: auto; width: min(320px, 86vw); z-index: 25;
    background: var(--bg); transform: translateX(-100%); transition: transform .2s ease; }
  body.nav-open .sidebar { transform: none; box-shadow: 0 10px 40px rgba(0,0,0,.18); }
  body.nav-open .scrim { display: block; position: fixed; inset: 56px 0 0 0; z-index: 20; background: rgba(0,0,0,.25); }
  .main { padding: 32px 16px 32px; }
}

/* Chapter */
.chapter, .home { max-width: 720px; margin: 0 auto; }
.kicker { font: 600 12px/1.4 var(--sans); text-transform: uppercase; letter-spacing: .07em; color: var(--accent-text); margin: 0 0 12px; }
h1, h2, h3, h4 { font-family: var(--sans); letter-spacing: -.02em; line-height: 1.2; color: var(--text); }
h1 { font-size: clamp(32px, 5vw, 44px); margin: 0 0 14px; font-weight: 700; }
.lede { font-size: 21px; line-height: 1.5; color: var(--muted); margin: 0 0 28px; }
.toc { border: 1px solid var(--line); border-radius: 10px; padding: 12px 16px; background: var(--surface); font: 14px/1.5 var(--sans); margin-bottom: 36px; }
.toc summary { cursor: pointer; font-weight: 600; color: var(--muted); }
.toc ol { margin: 10px 0 2px; padding-left: 22px; }
.toc li { margin: 3px 0; }
.toc a { color: var(--text); text-decoration: none; }
.toc a:hover { color: var(--accent-text); }

.prose h2 { font-size: 26px; margin: 52px 0 14px; padding-top: 8px; font-weight: 700; }
.prose h3 { font-size: 19px; margin: 34px 0 10px; font-weight: 600; }
.prose h4 { font-size: 16px; margin: 24px 0 8px; }
.prose p, .prose ul, .prose ol { margin: 0 0 16px; }
.prose li { margin: 5px 0; }
.prose li > ul, .prose li > ol { margin: 6px 0; }
.prose strong { font-weight: 700; }
.prose hr { border: 0; border-top: 1px solid var(--line); margin: 40px 0; }
.prose blockquote { margin: 24px 0; padding: 4px 0 4px 20px; border-left: 3px solid var(--accent); color: var(--muted); font-style: italic; font-size: 19px; }
.prose code { font: 14px/1.4 ui-monospace, "SF Mono", Menlo, monospace; background: var(--surface-2); padding: 2px 6px; border-radius: 5px; overflow-wrap: anywhere; }
.prose pre { background: var(--surface-2); border: 1px solid var(--line); border-radius: 10px; padding: 14px 16px; overflow-x: auto; }
.prose pre code { background: none; padding: 0; }
.anchor { margin-left: 8px; color: var(--faint); text-decoration: none; opacity: 0; font-weight: 400; }
h2:hover .anchor, h3:hover .anchor { opacity: 1; }

/* Tables */
.table-wrap { overflow-x: auto; margin: 20px 0 24px; border: 1px solid var(--line); border-radius: 10px; background: var(--surface); }
table { border-collapse: collapse; width: 100%; font: 14px/1.5 var(--sans); }
th, td { text-align: left; vertical-align: top; padding: 10px 12px; border-bottom: 1px solid var(--line); }
th { background: var(--surface-2); font-weight: 600; font-size: 13px; color: var(--muted); white-space: nowrap; }
tr:last-child td { border-bottom: 0; }
td:first-child { font-variant-numeric: tabular-nums; }

/* Callouts (admonitions) */
.admonition { margin: 24px 0; padding: 16px 18px; border-radius: 10px; background: var(--accent-soft); border: 1px solid color-mix(in srgb, var(--accent) 25%, transparent); font-size: 16px; }
.admonition > :last-child { margin-bottom: 0; }
.admonition-title { font: 700 12px/1.4 var(--sans); text-transform: uppercase; letter-spacing: .07em; color: var(--accent-text); margin: 0 0 8px !important; }
.admonition.formula { background: var(--surface); border: 1px solid var(--line); border-left: 4px solid var(--accent); }
.admonition.formula p:not(.admonition-title) { font: 600 17px/1.5 var(--sans); }
.admonition.takeaways { background: var(--good-soft); border-color: color-mix(in srgb, var(--good) 30%, transparent); }
.admonition.takeaways .admonition-title { color: var(--good); }
.admonition.warning { background: var(--warn-soft); border-color: color-mix(in srgb, var(--warn) 30%, transparent); }
.admonition.warning .admonition-title { color: var(--warn); }
.admonition.try { background: var(--surface); border: 1px dashed var(--accent); }

/* Pager */
.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin: 64px 0 0; font-family: var(--sans); }
.pager a { display: block; padding: 14px 16px; border: 1px solid var(--line); border-radius: 10px; background: var(--surface); text-decoration: none; color: var(--text); font-weight: 600; font-size: 15px; line-height: 1.35; }
.pager a:hover { border-color: var(--accent); }
.pager small { display: block; font-weight: 500; font-size: 12px; color: var(--faint); margin-bottom: 4px; }
.pager-next { text-align: right; }
@media (max-width: 520px) { .pager { grid-template-columns: 1fr; } .pager-next { text-align: left; } }

/* Home */
.hero { padding: 24px 0 8px; }
.hero h1 { font-size: clamp(40px, 8vw, 64px); }
.start { display: inline-block; margin: 0 0 12px; padding: 11px 18px; border-radius: 9px; background: var(--accent); color: #fff; text-decoration: none; font: 600 15px var(--sans); }
:root[data-theme="dark"] .start { color: #0d1a24; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .start { color: #0d1a24; } }
.part h2 { font: 600 12px/1.4 var(--sans); text-transform: uppercase; letter-spacing: .07em; color: var(--faint); margin: 44px 0 12px; }
.cards { display: grid; gap: 10px; }
.card { display: grid; grid-template-columns: 1fr auto; gap: 2px 12px; padding: 14px 16px; border: 1px solid var(--line); border-radius: 10px; background: var(--surface); text-decoration: none; color: var(--text); font-family: var(--sans); }
.card:hover { border-color: var(--accent); }
.card-num { grid-row: span 2; font-variant-numeric: tabular-nums; color: var(--faint); font-size: 14px; padding-top: 2px; }
.card-title { font-weight: 600; font-size: 16px; }
.card-meta { grid-row: 1; grid-column: 2; font-size: 12px; color: var(--faint); padding-top: 3px; white-space: nowrap; }
.card-lede { grid-column: 1 / 3; font-size: 14px; color: var(--muted); line-height: 1.45; }

.foot { max-width: 720px; margin: 72px auto 0; padding-top: 20px; border-top: 1px solid var(--line); font: 13px/1.6 var(--sans); color: var(--faint); }

@media (max-width: 640px) { .table-wrap table { min-width: 600px; } }

/* Lists: "easier > harder" */
.kicker a { color: inherit; text-decoration: none; }
.prose ol > li { margin: 0; padding: 10px 0; border-bottom: 1px solid var(--line); }
.prose ol > li:last-child { border-bottom: 0; }
.prose ol > li::marker { font: 600 13px var(--sans); color: var(--faint); font-variant-numeric: tabular-nums; }
.prose ol { padding-left: 34px; }
.prose ul > li::marker { color: var(--accent); }
.prose h2 + ul { padding: 14px 18px 14px 34px; background: var(--surface); border: 1px solid var(--line); border-left: 4px solid var(--accent); border-radius: 10px; }
.gt { font: 700 15px var(--sans); color: var(--week-now); padding: 0 2px; }
.keep { margin: 44px 0 0; padding: 16px 18px; border-radius: 10px; background: var(--good-soft); border: 1px solid color-mix(in srgb, var(--good) 30%, transparent); }
.keep p { margin: 0; }
.keep strong:first-child { display: block; font: 700 12px/1.4 var(--sans); text-transform: uppercase; letter-spacing: .07em; color: var(--good); margin-bottom: 6px; }
.part-blurb { margin: -6px 0 12px; font: 14px/1.5 var(--sans); color: var(--muted); }
.filter { width: 100%; margin: 4px 0 8px; padding: 12px 14px; font: 16px var(--sans); color: var(--text); background: var(--surface); border: 1px solid var(--line); border-radius: 10px; }
.filter:focus { outline: 2px solid var(--accent); outline-offset: 1px; }
.empty { font: 15px var(--sans); color: var(--muted); }
[hidden] { display: none !important; }
@media (max-width: 520px) {
  body { font-size: 18px; }
  .lede { font-size: 19px; }
  .prose ol { padding-left: 28px; }
  .prose h2 { font-size: 23px; margin-top: 40px; }
  .main { padding-bottom: calc(32px + env(safe-area-inset-bottom)); }
}