/* =========================================================================
   AI → Machine Learning Course — Shared Design System
   Standalone: no build tools. Linked relatively by every course page.
   ========================================================================= */

:root {
  /* Light palette */
  --bg:            #f7f6f3;
  --bg-elev:       #ffffff;
  --bg-sunken:     #efede8;
  --text:          #23201b;
  --text-soft:     #55504a;
  --text-faint:    #857f76;
  --border:        #e4e0d8;
  --border-strong: #d3cec4;

  --brand:         #b8562f;   /* terracotta */
  --brand-soft:    #f3e3da;
  --accent:        #2f6f6b;   /* teal */
  --accent-soft:   #dcebe9;

  --why:           #a8541f;
  --why-bg:        #f8ecdf;
  --intuition:     #3a6ea5;
  --intuition-bg:  #e4edf6;
  --math:          #6a4c93;
  --math-bg:       #ece5f4;
  --practice:      #2f7d4f;
  --practice-bg:   #e0f0e6;
  --limit:         #a23b52;
  --limit-bg:      #f8e3e8;
  --connect:       #8a6d1a;
  --connect-bg:    #f6efd8;

  --code-bg:       #2b2822;
  --code-text:     #f2ede3;

  --radius:        14px;
  --radius-sm:     9px;
  --shadow:        0 1px 2px rgba(0,0,0,.05), 0 8px 24px -12px rgba(0,0,0,.12);
  --maxw:          860px;

  --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-serif: "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --font-mono: "JetBrains Mono", "SF Mono", "Cascadia Code", Consolas, "Liberation Mono", monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg:            #17150f;
    --bg-elev:       #201d16;
    --bg-sunken:     #14120d;
    --text:          #ece7dc;
    --text-soft:     #b8b1a4;
    --text-faint:    #857f73;
    --border:        #322e25;
    --border-strong: #423d31;

    --brand:         #e0794f;
    --brand-soft:    #3a271d;
    --accent:        #5fb3ac;
    --accent-soft:   #1e3230;

    --why:           #e0965a;  --why-bg:       #33261a;
    --intuition:     #7fb0e0;  --intuition-bg: #1c2a38;
    --math:          #b79ce0;  --math-bg:      #281f38;
    --practice:      #74c78f;  --practice-bg:  #17301f;
    --limit:         #e08098;  --limit-bg:     #331d24;
    --connect:       #d8bd63;  --connect-bg:   #2f2913;

    --code-bg:       #0f0d09;
    --code-text:     #ece7dc;
    --shadow:        0 1px 2px rgba(0,0,0,.3), 0 10px 30px -14px rgba(0,0,0,.6);
  }
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 84px; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 17px;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* ---------- Top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.topbar-inner {
  max-width: var(--maxw); margin: 0 auto; padding: 12px 24px;
  display: flex; align-items: center; gap: 16px;
}
.topbar .brand-mark {
  font-weight: 700; letter-spacing: -.02em; color: var(--text);
  text-decoration: none; font-size: 15px; white-space: nowrap;
}
.topbar .brand-mark span { color: var(--brand); }
.topbar nav { margin-left: auto; display: flex; gap: 6px; flex-wrap: wrap; }
.topbar nav a {
  color: var(--text-soft); text-decoration: none; font-size: 14px;
  padding: 6px 12px; border-radius: 999px; transition: .15s;
}
.topbar nav a:hover { background: var(--bg-sunken); color: var(--text); }

/* ---------- Layout ---------- */
.wrap { max-width: var(--maxw); margin: 0 auto; padding: 48px 24px 120px; }

/* ---------- Hero ---------- */
.hero { margin-bottom: 40px; }
.eyebrow {
  display: inline-block; font-size: 13px; font-weight: 600; letter-spacing: .08em;
  text-transform: uppercase; color: var(--brand);
  background: var(--brand-soft); padding: 5px 12px; border-radius: 999px;
}
h1 {
  font-family: var(--font-serif);
  font-size: clamp(2rem, 5vw, 3rem); line-height: 1.1; letter-spacing: -.02em;
  margin: 18px 0 12px; font-weight: 600;
}
.lead { font-size: 1.2rem; color: var(--text-soft); max-width: 62ch; margin: 0; }

/* ---------- Typography ---------- */
h2 {
  font-family: var(--font-serif); font-weight: 600; letter-spacing: -.01em;
  font-size: 1.7rem; margin: 56px 0 8px; padding-top: 12px;
  border-top: 1px solid var(--border);
}
h3 { font-size: 1.28rem; font-weight: 650; margin: 36px 0 6px; letter-spacing: -.01em; }
h4 { font-size: 1.05rem; font-weight: 650; margin: 26px 0 4px; color: var(--text); }
p { margin: 14px 0; }
a { color: var(--brand); text-decoration-color: color-mix(in srgb, var(--brand) 35%, transparent); text-underline-offset: 3px; }
strong { font-weight: 650; }
ul, ol { padding-left: 1.3em; }
li { margin: 7px 0; }
hr { border: none; border-top: 1px solid var(--border); margin: 40px 0; }
small { color: var(--text-faint); }

blockquote {
  margin: 20px 0; padding: 4px 20px; border-left: 3px solid var(--border-strong);
  color: var(--text-soft); font-style: italic;
}

/* ---------- Callouts ---------- */
.callout {
  margin: 22px 0; padding: 16px 20px 16px 18px;
  border-radius: var(--radius-sm); border: 1px solid var(--border);
  border-left: 4px solid var(--c, var(--brand));
  background: var(--cbg, var(--bg-elev));
}
.callout .callout-label {
  font-size: 12px; font-weight: 700; letter-spacing: .06em; text-transform: uppercase;
  color: var(--c, var(--brand)); display: flex; align-items: center; gap: 8px;
  margin-bottom: 4px;
}
.callout p:first-of-type { margin-top: 4px; }
.callout p:last-child { margin-bottom: 0; }

.callout.why       { --c: var(--why);       --cbg: var(--why-bg); }
.callout.intuition { --c: var(--intuition); --cbg: var(--intuition-bg); }
.callout.math      { --c: var(--math);      --cbg: var(--math-bg); }
.callout.practice  { --c: var(--practice);  --cbg: var(--practice-bg); }
.callout.limit     { --c: var(--limit);     --cbg: var(--limit-bg); }
.callout.connect   { --c: var(--connect);   --cbg: var(--connect-bg); }
.callout.def       { --c: var(--accent);    --cbg: var(--accent-soft); }

/* ---------- Concept 8-step frame ---------- */
.frame {
  counter-reset: step; margin: 24px 0; border: 1px solid var(--border);
  border-radius: var(--radius); overflow: hidden; background: var(--bg-elev);
}
.frame .frame-row {
  display: grid; grid-template-columns: 44px 1fr; gap: 0;
  border-top: 1px solid var(--border);
}
.frame .frame-row:first-child { border-top: none; }
.frame .frame-row .n {
  background: var(--bg-sunken); display: flex; align-items: center; justify-content: center;
  font-weight: 700; color: var(--brand); font-size: 14px;
}
.frame .frame-row .c { padding: 12px 16px; }
.frame .frame-row .c b { display: block; font-size: .96rem; }
.frame .frame-row .c span { color: var(--text-soft); font-size: .93rem; }

/* ---------- Code ---------- */
pre {
  background: var(--code-bg); color: var(--code-text);
  border-radius: var(--radius-sm); padding: 18px 20px; overflow-x: auto;
  font-family: var(--font-mono); font-size: 14px; line-height: 1.6;
  margin: 20px 0; border: 1px solid rgba(255,255,255,.06);
}
pre code { font-family: inherit; background: none; padding: 0; color: inherit; }
code {
  font-family: var(--font-mono); font-size: .875em;
  background: var(--bg-sunken); padding: 2px 6px; border-radius: 5px;
  border: 1px solid var(--border);
}
.code-cap {
  font-size: 12px; color: var(--text-faint); margin: 18px 0 -12px;
  font-family: var(--font-mono);
}

/* comment / keyword tints (manual spans) */
.tok-c { color: #8b8577; font-style: italic; }
.tok-k { color: #e0794f; }
.tok-s { color: #8fbf7f; }
.tok-n { color: #7fb0e0; }

/* ---------- Math block ---------- */
.eq {
  font-family: var(--font-serif); font-size: 1.12rem; text-align: center;
  padding: 14px 16px; margin: 18px 0; background: var(--bg-sunken);
  border-radius: var(--radius-sm); overflow-x: auto; font-style: italic;
}
.eq .var { font-style: italic; }

/* ---------- Tables ---------- */
.tablewrap { overflow-x: auto; margin: 22px 0; }
table { border-collapse: collapse; width: 100%; font-size: .95rem; }
th, td { text-align: left; padding: 10px 14px; border-bottom: 1px solid var(--border); }
th { background: var(--bg-sunken); font-weight: 650; font-size: .82rem; letter-spacing: .04em; text-transform: uppercase; color: var(--text-soft); }
tbody tr:hover { background: var(--bg-elev); }

/* ---------- Roadmap module cards ---------- */
.modgrid { display: grid; gap: 18px; margin: 28px 0; }
.module {
  border: 1px solid var(--border); border-radius: var(--radius);
  background: var(--bg-elev); overflow: hidden; box-shadow: var(--shadow);
}
.module > header {
  display: flex; align-items: baseline; gap: 14px; padding: 18px 22px;
  border-bottom: 1px solid var(--border); background: var(--bg-sunken);
}
.module > header .mnum {
  font-family: var(--font-mono); font-size: 13px; font-weight: 700;
  color: #fff; background: var(--brand); border-radius: 8px;
  padding: 4px 10px; white-space: nowrap;
}
.module > header h3 { margin: 0; font-size: 1.15rem; }
.module > header .mtag { margin-left: auto; font-size: 12px; color: var(--text-faint); }
.lessons { list-style: none; margin: 0; padding: 6px 0; }
.lessons li { margin: 0; }
.lessons a, .lessons .li-static {
  display: flex; align-items: center; gap: 12px; padding: 10px 22px;
  text-decoration: none; color: var(--text); transition: .12s;
}
.lessons a:hover { background: var(--bg-sunken); }
.lessons .lnum {
  font-family: var(--font-mono); font-size: 12px; color: var(--text-faint);
  min-width: 26px;
}
.lessons .ltitle { flex: 1; }
.lessons .badge {
  font-size: 11px; font-weight: 600; padding: 2px 9px; border-radius: 999px;
  letter-spacing: .03em;
}
.badge.ready { background: var(--practice-bg); color: var(--practice); }
.badge.soon  { background: var(--bg-sunken); color: var(--text-faint); }
.badge.scratch { background: var(--math-bg); color: var(--math); }

/* ---------- Outcome / goal chips ---------- */
.chips { display: flex; flex-wrap: wrap; gap: 8px; margin: 16px 0; }
.chip {
  font-size: 13px; padding: 6px 12px; border-radius: 999px;
  background: var(--bg-elev); border: 1px solid var(--border); color: var(--text-soft);
}

/* ---------- Lesson nav footer ---------- */
.lessonnav {
  display: flex; gap: 14px; margin-top: 64px; padding-top: 28px;
  border-top: 1px solid var(--border);
}
.lessonnav a {
  flex: 1; text-decoration: none; padding: 16px 20px; border-radius: var(--radius);
  border: 1px solid var(--border); background: var(--bg-elev); transition: .15s;
}
.lessonnav a:hover { border-color: var(--brand); box-shadow: var(--shadow); }
.lessonnav .dir { font-size: 12px; color: var(--text-faint); text-transform: uppercase; letter-spacing: .06em; }
.lessonnav .ttl { display: block; margin-top: 3px; font-weight: 600; color: var(--text); }
.lessonnav a.next { text-align: right; }
.lessonnav a.disabled { opacity: .4; pointer-events: none; }

/* ---------- Meta / breadcrumb ---------- */
.crumb { font-size: 13px; color: var(--text-faint); margin-bottom: 8px; }
.crumb a { color: var(--text-soft); text-decoration: none; }
.crumb a:hover { color: var(--brand); }
.meta-row { display: flex; flex-wrap: wrap; gap: 18px; margin: 18px 0 0; font-size: 13px; color: var(--text-faint); }
.meta-row b { color: var(--text-soft); font-weight: 600; }

/* ---------- Checklist ---------- */
.checklist { list-style: none; padding-left: 0; }
.checklist li { padding-left: 30px; position: relative; }
.checklist li::before {
  content: "✓"; position: absolute; left: 0; top: 0;
  color: var(--practice); font-weight: 700;
}

/* ---------- Exercise box ---------- */
.exercise {
  border: 1px dashed var(--border-strong); border-radius: var(--radius);
  padding: 18px 22px; margin: 22px 0; background: var(--bg-elev);
}
.exercise > .x-h {
  font-size: 12px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase;
  color: var(--accent); margin-bottom: 6px;
}

/* ---------- Footer ---------- */
.foot { max-width: var(--maxw); margin: 0 auto; padding: 30px 24px 60px; color: var(--text-faint); font-size: 13px; border-top: 1px solid var(--border); }
.foot a { color: var(--text-soft); text-decoration-color: color-mix(in srgb, var(--text-soft) 35%, transparent); }
.foot a:hover { color: var(--brand); }
.foot .byline { display: block; margin-top: 14px; }

/* details/summary */
details { margin: 18px 0; border: 1px solid var(--border); border-radius: var(--radius-sm); background: var(--bg-elev); }
summary { cursor: pointer; padding: 12px 18px; font-weight: 600; }
details[open] summary { border-bottom: 1px solid var(--border); }
details .details-body { padding: 4px 18px 14px; }

@media (max-width: 640px) {
  body { font-size: 16px; }
  .wrap { padding: 32px 18px 100px; }
  .lessonnav { flex-direction: column; }
}