/* AI-ML Course — every layer of AI engineering, 5 levels deep */
:root {
  --bg: #0b0f19; --surface: #111827; --card: #151c2e; --border: rgba(255,255,255,.08);
  --text: #f9fafb; --muted: #9ca3af; --dim: #6b7280;
  --pri: #3b82f6; --vio: #8b5cf6; --cyan: #06b6d4; --green: #10b981; --amber: #f59e0b; --red: #f87171;
  --grad: linear-gradient(135deg, #3b82f6, #8b5cf6);
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body { background: var(--bg); color: var(--text); font-family: 'Segoe UI', system-ui, sans-serif; line-height: 1.65; }
a { color: inherit; text-decoration: none; }
.wrap { width: min(100% - 32px, 1100px); margin-inline: auto; }

/* header / footer */
.site { position: sticky; top: 0; z-index: 50; background: rgba(11,15,25,.88); backdrop-filter: blur(10px); border-bottom: 1px solid var(--border); padding: 12px 0; }
.site .wrap { display: flex; align-items: center; justify-content: space-between; gap: 12px; }
.brand { font-weight: 800; font-size: 1.1rem; background: linear-gradient(90deg,#fff,#93c5fd); -webkit-background-clip: text; -webkit-text-fill-color: transparent; }
.nav { display: flex; gap: 18px; align-items: center; flex-wrap: wrap; }
.nav a { color: var(--muted); font-size: .9rem; transition: color .2s; }
.nav a:hover { color: var(--text); }
.foot { border-top: 1px solid var(--border); margin-top: 56px; padding: 28px 0 40px; text-align: center; color: var(--dim); font-size: .85rem; }
.foot a { color: var(--cyan); margin: 0 8px; }
.foot a:hover { text-decoration: underline; }

/* c-hero / meta (chapter top banner) */
.c-hero { text-align: center; padding: 44px 0 22px; }
.c-hero h1 { font-size: clamp(1.9rem, 4.5vw, 2.7rem); background: linear-gradient(90deg,#fff,#93c5fd); -webkit-background-clip: text; -webkit-text-fill-color: transparent; }
.c-hero .sub { color: var(--muted); max-width: 680px; margin: 10px auto 0; font-size: 1.02rem; }
.c-meta { display: flex; flex-wrap: wrap; gap: 14px; justify-content: center; margin-top: 16px; }
.c-meta span { background: var(--card); border: 1px solid var(--border); border-radius: 99px; padding: 6px 14px; font-size: .82rem; color: var(--muted); }
.c-meta b { color: var(--cyan); }
.c-head { background: var(--surface); border: 1px solid var(--border); border-radius: 14px; padding: 18px 20px; margin-bottom: 18px; }
.c-head .emoji { font-size: 1.5rem; }
.c-head .tag { display: inline-block; font-size: .7rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--cyan); background: rgba(6,182,212,.12); border: 1px solid rgba(6,182,212,.3); padding: 3px 10px; border-radius: 99px; margin-bottom: 8px; }
.c-head h1 { font-size: 1.55rem; margin: 0 0 4px; }
.c-head .t { color: var(--muted); font-size: .92rem; margin-bottom: 10px; }
.c-head .app-row { display: flex; flex-wrap: wrap; gap: 6px; }
/* chapter body */
.c-body { margin-top: 6px; }
.lvltabs { display: flex; gap: 6px; flex-wrap: wrap; margin: 18px 0 14px; background: var(--card); border: 1px solid var(--border); border-radius: 12px; padding: 10px 12px; }
.lvltabs button { flex: 1 1 auto; background: transparent; border: none; color: var(--muted); font-size: .84rem; font-weight: 600; padding: 6px 10px; border-radius: 8px; cursor: pointer; transition: all .18s; }
.lvltabs button.active { background: rgba(59,130,246,.18); color: var(--text); }
.lvltabs button:hover { color: var(--text); }
.panel { margin-top: 8px; }
.panel h2 { font-size: 1.15rem; color: var(--cyan); margin-bottom: 10px; }
.panel .analogy { background: rgba(245,158,11,.08); border-left: 3px solid var(--amber); border-radius: 8px; padding: 12px 14px; margin: 12px 0; }
.panel .analogy .lbl { display: block; font-size: .72rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--amber); margin-bottom: 4px; }
.panel .reallife { background: rgba(6,182,212,.07); border-left: 3px solid var(--cyan); border-radius: 8px; padding: 12px 14px; margin: 12px 0; }
.panel .reallife .lbl { display: block; font-size: .72rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--cyan); margin-bottom: 4px; }
.panel p { margin: 6px 0; color: var(--muted); }
.panel b, .panel strong { color: var(--text); }
.panel code { background: rgba(255,255,255,.06); padding: 1px 6px; border-radius: 4px; font-size: .85rem; color: var(--cyan); }
.panel pre { background: #0a0e16; border: 1px solid var(--border); border-radius: 10px; padding: 14px 16px; overflow-x: auto; margin: 10px 0; font-size: .82rem; color: #c9d1d9; line-height: 1.5; }
.panel pre code { background: none; padding: 0; color: inherit; }
.panel .try { margin-top: 14px; display: flex; gap: 8px; flex-wrap: wrap; }
.panel .try a { display: inline-flex; align-items: center; gap: 6px; background: rgba(59,130,246,.12); border: 1px solid rgba(59,130,246,.3); color: var(--cyan); padding: 8px 14px; border-radius: 9px; font-size: .82rem; font-weight: 600; transition: all .18s; }
.panel .try a:hover { background: rgba(59,130,246,.22); color: #fff; }
.lvlnav { display: flex; justify-content: space-between; gap: 10px; margin-top: 16px; }
.lvlnav button { background: var(--card); border: 1px solid var(--border); color: var(--text); padding: 9px 16px; border-radius: 9px; font-size: .84rem; font-weight: 600; cursor: pointer; transition: all .18s; }
.lvlnav button:hover:not(:disabled) { border-color: var(--cyan); color: var(--cyan); }
.lvlnav button:disabled { opacity: .35; cursor: default; }

/* quiz */
.quiz { margin-top: 22px; background: var(--card); border: 1px solid var(--border); border-radius: 14px; padding: 18px 20px; }
.quiz h3 { font-size: 1.05rem; margin-bottom: 12px; }
.qq { border: 1px solid var(--border); border-radius: 10px; padding: 12px 14px; margin: 10px 0; background: rgba(255,255,255,.02); }
.qq .q { font-size: .92rem; color: var(--text); margin-bottom: 8px; font-weight: 600; }
.qq label { display: block; padding: 5px 8px; border-radius: 6px; margin: 3px 0; cursor: pointer; font-size: .86rem; color: var(--muted); transition: all .15s; }
.qq label:hover { background: rgba(255,255,255,.05); }
.qq input:checked + label { background: rgba(59,130,246,.16); color: var(--text); font-weight: 600; }
.qq .why { margin-top: 8px; font-size: .82rem; padding: 6px 10px; border-radius: 6px; display: none; }
.qq .why.ok { display: block; background: rgba(16,185,129,.12); color: var(--green); }
.qq .why.bad { display: block; background: rgba(248,113,113,.12); color: var(--red); }
.quiz .score { margin-top: 12px; font-size: .92rem; color: var(--green); font-weight: 700; }
.quiz .score.all { color: var(--amber); }
.quiz .hint { font-size: .78rem; color: var(--dim); margin-top: 6px; }

/* crumbs */
.crumb { font-size: .78rem; color: var(--muted); margin: 0 0 10px; }
.crumb a { color: var(--cyan); }
.prog-wrap { background: var(--card); border: 1px solid var(--border); border-radius: 12px; padding: 14px 18px; margin: 18px 0; }
.prog-track { height: 8px; background: #1e2638; border-radius: 99px; overflow: hidden; }
.prog-fill { height: 100%; background: var(--grad); transition: width .5s ease; }
.prog-txt { color: var(--muted); font-size: .85rem; margin-top: 8px; }
.chgrid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 16px; padding: 10px 0 6px; }
@media (max-width: 760px) { .chgrid { grid-template-columns: 1fr; } }
.chcard { display: block; background: var(--card); border: 1px solid var(--border); border-radius: 16px; padding: 18px; transition: transform .18s ease, border-color .18s ease; text-decoration: none; color: inherit; }
.chcard:hover { transform: translateY(-3px); border-color: rgba(59,130,246,.5); }
.chcard .done-badge { position: absolute; top: 14px; right: 14px; font-size: 1.1rem; }
.chcard .emoji { font-size: 1.5rem; display: block; margin-bottom: 6px; }
.chcard .tag { display: inline-block; font-size: .7rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--cyan); background: rgba(6,182,212,.12); border: 1px solid rgba(6,182,212,.3); padding: 3px 10px; border-radius: 99px; margin-bottom: 8px; }
.chcard h3 { font-size: 1.1rem; margin: 0 0 4px; }
.chcard .t { color: var(--muted); font-size: .86rem; min-height: 2.4em; margin-bottom: 10px; }
.chcard .apps { margin-bottom: 10px; }
.chcard .lvlchips { display: flex; gap: 4px; flex-wrap: wrap; }
.chip { display: inline-block; width: 24px; height: 22px; line-height: 22px; text-align: center; font-size: .66rem; font-weight: 700; color: var(--muted); background: #1e2638; border: 1px solid var(--border); border-radius: 6px; }
.chip.done { background: rgba(16,185,129,.18); color: var(--green); border-color: rgba(16,185,129,.4); }
.chcard { position: relative; }
.chcard .open { display: block; font-size: .82rem; color: var(--cyan); margin-top: 8px; }

/* ============================================================
   Parts 6-9 additions — shared renderer (/assets/course.js)
   ============================================================ */

/* 📐 "Standard, not from-scratch" callout — used at Level 2 of every chapter */
.panel .standard { background: rgba(139,92,246,.09); border-left: 3px solid var(--vio); border-radius: 8px; padding: 12px 14px; margin: 12px 0; }
.panel .standard .lbl { display: block; font-size: .72rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: #c4b5fd; margin-bottom: 4px; }

/* chapter header (existing parts leave .ch-head unstyled; give it the card look) */
.ch-head { display: flex; gap: 14px; align-items: flex-start; background: var(--surface); border: 1px solid var(--border); border-radius: 14px; padding: 18px 20px; margin-bottom: 4px; }
.ch-head .emoji { font-size: 1.6rem; line-height: 1; }
.ch-head h1 { font-size: 1.5rem; margin: 4px 0; }
.ch-head .t { color: var(--muted); font-size: .92rem; margin-bottom: 10px; }
.ch-head .app-row { display: flex; flex-wrap: wrap; gap: 6px; }
.app-chip { display: inline-block; font-size: .72rem; color: var(--muted); background: rgba(255,255,255,.05); border: 1px solid var(--border); border-radius: 99px; padding: 3px 10px; }

/* hub: "standard, not from-scratch" note + resume button */
.foot-note { max-width: 720px; margin: 14px auto 0; padding: 10px 16px; font-size: .86rem; color: var(--muted); background: rgba(139,92,246,.07); border: 1px solid rgba(139,92,246,.25); border-radius: 10px; text-align: center; }
.foot-note b { color: #c4b5fd; }
.hub-resume { display: inline-flex; align-items: center; gap: 8px; margin-top: 12px; background: var(--grad); color: #fff; font-weight: 700; font-size: .9rem; padding: 10px 18px; border-radius: 10px; border: none; cursor: pointer; }
.hub-resume:hover { filter: brightness(1.08); }

/* "Recommended next" card — keeps the learner moving */
.nextcard { display: block; margin: 22px 0 6px; background: linear-gradient(135deg, rgba(59,130,246,.12), rgba(139,92,246,.12)); border: 1px solid rgba(139,92,246,.3); border-radius: 14px; padding: 16px 18px; color: inherit; transition: border-color .18s ease, transform .18s ease; }
.nextcard:hover { border-color: rgba(139,92,246,.6); transform: translateY(-2px); }
.nextcard .kick { display: block; font-size: .72rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--vio); margin-bottom: 4px; }
.nextcard .nt { font-size: 1.05rem; font-weight: 700; color: var(--text); }
.nextcard .nd { display: block; color: var(--muted); font-size: .86rem; margin-top: 3px; }

/* prev / next chapter strip */
.chapnav { display: flex; justify-content: space-between; gap: 10px; margin: 16px 0 4px; }
.chapnav a, .chapnav span { flex: 1; background: var(--card); border: 1px solid var(--border); border-radius: 10px; padding: 10px 14px; font-size: .82rem; color: var(--muted); }
.chapnav a:hover { border-color: var(--cyan); color: var(--cyan); }
.chapnav .nx { text-align: right; }
.chapnav .disabled { opacity: .35; }

/* lazy-load placeholder */
.ch-loading { text-align: center; color: var(--muted); padding: 60px 0; font-size: .92rem; }
.ch-loading::before { content: "⏳"; display: block; font-size: 1.6rem; margin-bottom: 8px; }
.ch-error { text-align: center; color: var(--red); padding: 60px 0; }

/* full-path strip (hub) */
.pathstrip { display: flex; flex-wrap: wrap; gap: 6px; justify-content: center; margin: 16px 0 0; }
.pathstrip a, .pathstrip span { font-size: .74rem; padding: 4px 9px; border-radius: 99px; border: 1px solid var(--border); color: var(--muted); background: var(--card); }
.pathstrip .cur { color: var(--text); border-color: var(--vio); background: rgba(139,92,246,.15); font-weight: 700; }
.pathstrip a:hover { color: var(--text); border-color: var(--cyan); }