/* The Quantum Engineer — zero-dependency stylesheet. No webfonts are fetched
   from the internet: Latin text uses local system stacks; Farsi uses the
   bundled Sahel font (SIL OFL 1.1, see fonts/OFL.txt), served from this site. */

@font-face {
  font-family: "Sahel";
  src: url("fonts/Sahel.woff2") format("woff2");
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}
@font-face {
  font-family: "Sahel";
  src: url("fonts/Sahel-Bold.woff2") format("woff2");
  font-weight: 700;
  font-style: normal;
  font-display: swap;
}

:root {
  --bg: #faf9f6;
  --fg: #21201d;
  --muted: #6f6a61;
  --accent: #5b4fd6;
  --accent-fg: #ffffff;
  --accent-soft: #efecff;
  --line: #e5e2da;
  --card: #ffffff;
  --code-bg: #f0eee8;
  --code-fg: #2b2a27;
  --mark: #ffe9a8;
  --shadow: 0 1px 3px rgba(30, 25, 60, .08);
  --sidebar-w: 300px;
  --serif: "Iowan Old Style", "Palatino", Georgia, "Times New Roman", serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  --fa: "Sahel", -apple-system, BlinkMacSystemFont, "Segoe UI", Tahoma, Arial, sans-serif;
}
[data-theme="dark"] {
  --bg: #15151b;
  --fg: #e7e5e1;
  --muted: #98948c;
  --accent: #948bff;
  --accent-fg: #17172a;
  --accent-soft: #24233c;
  --line: #2b2b34;
  --card: #1b1b22;
  --code-bg: #1e1e28;
  --code-fg: #e2e0dc;
  --mark: #5c4d14;
  --shadow: 0 1px 3px rgba(0, 0, 0, .4);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: var(--sans);
  font-size: 16px;
}
[dir="rtl"] body, body:lang(fa) {
  font-family: var(--fa);
}

/* ---------- layout ---------- */
#app { min-height: 100vh; }

#sidebar {
  position: fixed;
  inset-block: 0;
  inset-inline-start: 0;
  width: var(--sidebar-w);
  display: flex;
  flex-direction: column;
  background: var(--card);
  border-inline-end: 1px solid var(--line);
  z-index: 20;
}
#main {
  margin-inline-start: var(--sidebar-w);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
#content {
  width: 100%;
  max-width: 760px;
  margin: 0 auto;
  padding: 3rem 2.2rem 5rem;
  outline: none;
}

/* ---------- sidebar ---------- */
.side-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: .5rem;
  padding: .9rem 1rem .8rem;
  border-bottom: 1px solid var(--line);
}
.brand {
  display: flex;
  align-items: center;
  gap: .55rem;
  text-decoration: none;
  color: var(--fg);
  line-height: 1.15;
}
.brand-mark {
  font-size: 1.5rem;
  color: var(--accent);
  line-height: 1;
}
.brand-text {
  font-family: var(--serif);
  font-size: .95rem;
  font-weight: 700;
  letter-spacing: .01em;
}
.side-controls { display: flex; gap: .3rem; }
.ctl {
  border: 1px solid var(--line);
  background: var(--bg);
  color: var(--fg);
  border-radius: 7px;
  min-width: 2rem;
  height: 2rem;
  padding: 0 .5rem;
  font: 600 .82rem var(--sans);
  cursor: pointer;
}
.ctl:hover { border-color: var(--accent); color: var(--accent); }

.search-wrap { padding: .7rem 1rem; border-bottom: 1px solid var(--line); }
#search {
  width: 100%;
  padding: .45rem .7rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--bg);
  color: var(--fg);
  font: .88rem var(--sans);
}
#search:focus { outline: 2px solid var(--accent-soft); border-color: var(--accent); }
#search-status { display: block; font: .72rem var(--sans); color: var(--muted); padding: .3rem 0 0; }

#toc { flex: 1; overflow-y: auto; padding: .6rem .5rem 1rem; }
.toc-part { margin: .1rem 0; }
.toc-part > button {
  display: flex;
  align-items: baseline;
  gap: .5rem;
  width: 100%;
  text-align: start;
  border: 0;
  background: none;
  color: var(--fg);
  font: 500 .845rem/1.35 var(--sans);
  padding: .42rem .55rem;
  border-radius: 8px;
  cursor: pointer;
}
.toc-part > button:hover { background: var(--accent-soft); }
.toc-part > button .pnum {
  flex: none;
  min-width: 1.6em;
  font: 700 .72rem var(--mono);
  color: var(--accent);
}
.toc-part.open > button { color: var(--accent); background: var(--accent-soft); }
.toc-chs { display: none; padding: .1rem 0 .35rem calc(1.05rem + .55rem); }
[dir="rtl"] .toc-chs { padding-inline-start: 0; padding-inline-end: calc(1.05rem + .55rem); }
.toc-part.open .toc-chs { display: block; }
.toc-chs a {
  display: block;
  color: var(--muted);
  text-decoration: none;
  font: .8rem/1.4 var(--sans);
  padding: .28rem .5rem;
  border-radius: 7px;
}
.toc-chs a:hover { color: var(--fg); background: var(--accent-soft); }
.toc-chs a.active { color: var(--accent); font-weight: 600; }
.toc-sec-count { color: var(--muted); font-size: .74rem; }
.toc-loading { color: var(--muted); font: .78rem var(--sans); padding: .4rem .6rem; }

.search-results .sr {
  display: block;
  text-decoration: none;
  color: var(--fg);
  padding: .45rem .55rem;
  border-radius: 8px;
  font: .8rem/1.45 var(--sans);
}
.search-results .sr:hover { background: var(--accent-soft); }
.search-results .sr .sr-where { color: var(--accent); font-weight: 600; font-size: .72rem; }
.search-results .sr .sr-snip { color: var(--muted); }
.search-results mark { background: var(--mark); color: inherit; border-radius: 2px; padding: 0 1px; }

.side-foot {
  display: flex;
  gap: .4rem;
  align-items: center;
  padding: .7rem 1rem;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font: .76rem var(--sans);
}
.side-foot a { color: var(--muted); }
.side-foot a:hover { color: var(--accent); }

#scrim {
  position: fixed; inset: 0;
  background: rgba(10, 10, 20, .45);
  z-index: 15;
}

/* ---------- topbar (mobile) ---------- */
#topbar {
  display: none;
  position: sticky;
  top: 0;
  z-index: 10;
  align-items: center;
  gap: .7rem;
  padding: .55rem .9rem;
  background: var(--card);
  border-bottom: 1px solid var(--line);
  font: 600 .9rem var(--sans);
}

/* ---------- article typography ---------- */
#content { font-family: var(--serif); font-size: 1.06rem; line-height: 1.75; }
[dir="rtl"] #content { font-family: var(--fa); font-size: 1.02rem; line-height: 2.05; }

.crumb {
  font-family: var(--sans);
  font-size: .78rem;
  letter-spacing: .02em;
  color: var(--muted);
  margin-bottom: 1.4rem;
}
.crumb a { color: var(--muted); text-decoration: none; }
.crumb a:hover { color: var(--accent); }
.crumb .sep { margin: 0 .45em; color: var(--line); }

#content h1 {
  font-family: var(--serif);
  font-size: 2.05rem;
  line-height: 1.2;
  margin: 0 0 1.4rem;
  letter-spacing: -.01em;
}
[dir="rtl"] #content h1 { font-family: var(--fa); font-size: 1.7rem; }
#content h2 {
  font-family: var(--serif);
  font-size: 1.45rem;
  margin: 2.6rem 0 1rem;
  line-height: 1.25;
}
[dir="rtl"] #content h2 { font-family: var(--fa); font-size: 1.3rem; }
#content h3 {
  font-family: var(--sans);
  font-size: 1.06rem;
  margin: 2.2rem 0 .7rem;
  line-height: 1.35;
}
#content h3 .secnum { color: var(--accent); font-family: var(--mono); font-size: .88em; margin-inline-end: .55em; }
#content h4 { font-family: var(--sans); font-size: .95rem; margin: 1.6rem 0 .5rem; }
#content p { margin: 0 0 1.05rem; }
#content a { color: var(--accent); text-decoration: underline; text-decoration-color: color-mix(in srgb, var(--accent) 40%, transparent); text-underline-offset: 2px; }
#content strong { font-weight: 700; }
#content em { font-style: italic; }
[dir="rtl"] #content em { font-style: normal; }

#content code {
  font-family: var(--mono);
  font-size: .84em;
  background: var(--code-bg);
  color: var(--code-fg);
  border-radius: 5px;
  padding: .12em .38em;
  direction: ltr;
  unicode-bidi: embed;
}
#content pre {
  background: var(--code-bg);
  color: var(--code-fg);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: .9rem 1.1rem;
  overflow-x: auto;
  direction: ltr;
  text-align: left;
  line-height: 1.55;
  margin: 0 0 1.2rem;
}
#content pre code { background: none; padding: 0; font-size: .8rem; }

#content ul, #content ol { margin: 0 0 1.1rem; padding-inline-start: 1.5rem; }
#content li { margin: .3rem 0; }
#content hr { border: 0; border-top: 1px solid var(--line); margin: 2.4rem 0; }

#content table {
  border-collapse: collapse;
  width: 100%;
  font-family: var(--sans);
  font-size: .84rem;
  margin: 0 0 1.3rem;
}
#content th, #content td {
  border: 1px solid var(--line);
  padding: .45rem .65rem;
  text-align: start;
  vertical-align: top;
}
#content th { background: var(--accent-soft); font-weight: 600; }
#content tbody tr:nth-child(even) { background: color-mix(in srgb, var(--card) 60%, var(--bg)); }

/* ---------- callouts ---------- */
.callout {
  border: 1px solid var(--line);
  border-inline-start: 3px solid var(--accent);
  background: var(--card);
  border-radius: 10px;
  padding: .85rem 1.1rem;
  margin: 0 0 1.3rem;
  box-shadow: var(--shadow);
  font-family: var(--sans);
  font-size: .92rem;
}
.callout > *:last-child { margin-bottom: 0; }
.callout .co-title {
  display: block;
  font: 700 .74rem var(--sans);
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 0 0 .5rem;
}
.callout p, .callout ul, .callout ol { margin-bottom: .6rem; font-size: .92rem; }
.callout pre { font-size: .78rem; margin-bottom: .7rem; }
.callout.note    { border-inline-start-color: #4a90d9; } .callout.note    .co-title { color: #4a90d9; }
.callout.tip     { border-inline-start-color: #2e9e6b; } .callout.tip     .co-title { color: #2e9e6b; }
.callout.experiment { border-inline-start-color: #d9822b; } .callout.experiment .co-title { color: #d9822b; }
.callout.research   { border-inline-start-color: #b05590; } .callout.research   .co-title { color: #b05590; }
.callout.warning { border-inline-start-color: #c94f4f; } .callout.warning .co-title { color: #c94f4f; }
.callout.levels {
  border-inline-start-color: var(--accent);
  background: linear-gradient(0deg, var(--accent-soft), var(--card));
}

/* ---------- section pill nav & pager ---------- */
.sec-nav {
  display: flex;
  flex-wrap: wrap;
  gap: .35rem;
  margin: 0 0 1.8rem;
  padding: .7rem 0 0;
  border-top: 1px solid var(--line);
  font-family: var(--sans);
}
.sec-nav a {
  font-size: .76rem;
  color: var(--muted);
  text-decoration: none;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: .18rem .6rem;
}
.sec-nav a:hover { color: var(--accent); border-color: var(--accent); }

.pager {
  display: flex;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 1.2rem;
  border-top: 1px solid var(--line);
  font-family: var(--sans);
}
.pager a {
  flex: 1;
  text-decoration: none;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: .7rem .9rem;
  color: var(--fg);
  background: var(--card);
}
.pager a:hover { border-color: var(--accent); }
.pager a .pg-label { display: block; font-size: .7rem; letter-spacing: .08em; text-transform: uppercase; color: var(--muted); margin-bottom: .2rem; }
.pager a .pg-title { font-size: .88rem; font-weight: 600; }
.pager a.next { text-align: end; margin-inline-start: auto; }
.pager a.next .pg-title { }

/* ---------- home / part landing ---------- */
.hero-sub { font-size: 1.15rem; color: var(--muted); margin-top: -.6rem; }
.part-cards { display: grid; grid-template-columns: 1fr; gap: .6rem; margin: 1.4rem 0; }
.part-cards a {
  display: flex;
  gap: .8rem;
  align-items: baseline;
  text-decoration: none;
  color: var(--fg);
  border: 1px solid var(--line);
  background: var(--card);
  border-radius: 10px;
  padding: .7rem .9rem;
  font-family: var(--sans);
  font-size: .9rem;
}
.part-cards a:hover { border-color: var(--accent); }
.part-cards .pnum { flex: none; min-width: 2.2em; font: 700 .78rem var(--mono); color: var(--accent); }
.ch-cards { margin: 1.2rem 0 2rem; padding: 0; list-style: none; }
.ch-cards li a {
  display: flex;
  gap: .7rem;
  align-items: baseline;
  text-decoration: none;
  color: var(--fg);
  border-bottom: 1px solid var(--line);
  padding: .6rem .2rem;
  font-family: var(--sans);
  font-size: .92rem;
}
.ch-cards li a:hover { color: var(--accent); }
.ch-cards .cnum { flex: none; min-width: 2.4em; font: 600 .78rem var(--mono); color: var(--accent); }

.status-pill {
  display: inline-block;
  font: 600 .72rem var(--sans);
  color: var(--accent);
  background: var(--accent-soft);
  border-radius: 999px;
  padding: .15rem .7rem;
  margin-bottom: 1rem;
}

/* ---------- misc ---------- */
.err-panel {
  border: 1px solid var(--line);
  background: var(--card);
  border-radius: 12px;
  padding: 1.4rem;
  font-family: var(--sans);
}
.err-panel code { font-size: .85em; }

mark { background: var(--mark); color: inherit; padding: 0 1px; border-radius: 2px; }

/* ---------- rtl ---------- */
[dir="rtl"] .brand-text, [dir="rtl"] #content h1, [dir="rtl"] #content h2 { letter-spacing: 0; }
[dir="rtl"] pre, [dir="rtl"] #content code { text-align: left; }

/* ---------- responsive ---------- */
@media (max-width: 920px) {
  #sidebar {
    transform: translateX(-102%);
    transition: transform .25s ease;
    box-shadow: var(--shadow);
  }
  [dir="rtl"] #sidebar { transform: translateX(102%); }
  body.nav-open #sidebar { transform: none; }
  #main { margin-inline-start: 0; }
  #topbar { display: flex; }
  #content { padding: 1.6rem 1.1rem 4rem; }
}
body.nav-open #scrim { display: block; }

/* ---------- print ---------- */
@media print {
  #sidebar, #topbar, #scrim, .sec-nav, .pager, .side-foot { display: none !important; }
  #main { margin: 0; }
  #content { max-width: none; padding: 0; }
  body { background: #fff; color: #000; }
}