/* ═══════════════════════════════════════════════════════════════
   Apple-style Design System  ·  Git Start Book
   Palette: apple.com neutrals + subtle green tint
   ═══════════════════════════════════════════════════════════════ */

/* ── Tokens ────────────────────────────────────────────────────── */
:root {
  --white:        #ffffff;
  --bg:           #f5f7f5;   /* apple #f5f5f7 + green tint */
  --bg-alt:       #eef2ee;   /* tinted band */
  --text:         #1a1c1a;   /* apple #1d1d1f + green */
  --text-2:       #6b706b;   /* apple #6e6e73 + green */
  --border:       #d0d5d0;   /* apple #d2d2d7 + green */
  --green:        #1a7a45;   /* CTA green */
  --green-light:  #e8f3ec;
  --green-mid:    #b8d9c5;
  --shadow-1: 0 2px 8px rgba(0,0,0,.06);
  --shadow-2: 0 8px 24px rgba(0,0,0,.08);
  --r:    12px;
  --r-lg: 20px;
  --max:  980px;
  --nav:  48px;
}

/* ── Reset ─────────────────────────────────────────────────────── */
*,*::before,*::after{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  font-family:-apple-system,BlinkMacSystemFont,"Noto Sans TC","Helvetica Neue",Arial,sans-serif;
  font-size:17px;
  line-height:1.6;
  color:var(--text);
  background:var(--white);
  -webkit-font-smoothing:antialiased;
}
a{color:inherit;text-decoration:none}
img{max-width:100%;display:block}
ul,ol{margin:0;padding:0;list-style:none}
p{margin:0}
h1,h2,h3{margin:0}

/* ── Shell ─────────────────────────────────────────────────────── */
.site-shell{width:100%;overflow-x:hidden}

/* ── Nav ───────────────────────────────────────────────────────── */
.topbar{
  position:sticky;top:0;z-index:100;
  display:flex;align-items:center;justify-content:space-between;
  height:var(--nav);
  padding:0 max(22px,calc((100% - var(--max))/2 + 22px));
  background:rgba(255,255,255,.88);
  border-bottom:1px solid rgba(208,213,208,.7);
  backdrop-filter:saturate(180%) blur(20px);
  -webkit-backdrop-filter:saturate(180%) blur(20px);
}
.brand{display:inline-flex;align-items:center;gap:9px}
.brand-mark{
  display:inline-grid;place-items:center;
  width:28px;height:28px;border-radius:7px;
  background:linear-gradient(145deg,var(--green-mid),var(--green));
  font-size:0.68rem;font-weight:700;color:#fff;letter-spacing:-0.02em;
}
.brand-copy{display:grid;gap:0;line-height:1.15}
.brand-copy strong{font-size:0.82rem;font-weight:600;letter-spacing:-0.02em}
.brand-copy span{font-size:0.66rem;color:var(--text-2)}
.site-nav{display:flex;align-items:center}
.site-nav a{
  padding:5px 12px;border-radius:999px;
  font-size:0.8rem;font-weight:500;color:var(--text-2);
  transition:color 120ms,background 120ms;
}
.site-nav a:hover{color:var(--text);background:var(--green-light)}
.site-nav a[aria-current="page"]{color:var(--text);font-weight:600}
.nav-toggle{
  display:none;border:0;cursor:pointer;
  font:inherit;font-size:0.8rem;font-weight:500;
  padding:5px 12px;border-radius:999px;
  color:var(--text);background:var(--bg);
}

/* ── Helpers ───────────────────────────────────────────────────── */
.wrap{width:min(calc(100% - 44px),var(--max));margin:0 auto}
.eyebrow{
  display:inline-block;margin:0 0 12px;
  padding:3px 10px;border-radius:999px;
  border:1px solid var(--green-mid);background:var(--green-light);
  color:var(--green);font-size:0.68rem;font-weight:600;
  letter-spacing:.09em;text-transform:uppercase;
}
.card-kicker{
  display:block;margin:0 0 8px;
  color:var(--text-2);font-size:0.72rem;font-weight:600;
  letter-spacing:.06em;text-transform:uppercase;
}

/* ── Buttons ───────────────────────────────────────────────────── */
.button{
  display:inline-flex;align-items:center;justify-content:center;
  height:40px;padding:0 20px;border-radius:999px;border:none;cursor:pointer;
  font:inherit;font-size:0.84rem;font-weight:600;letter-spacing:-0.01em;
  transition:opacity 140ms,transform 140ms;
}
.button:hover{opacity:.84;transform:translateY(-1px)}
.button-primary{background:var(--text);color:#fff}
.button-secondary{background:var(--white);color:var(--text);border:1px solid var(--border);box-shadow:var(--shadow-1)}

/* ── Hero ──────────────────────────────────────────────────────── */
.hero{
  display:grid;grid-template-columns:1.1fr 0.9fr;gap:40px;align-items:center;
  width:min(calc(100% - 44px),var(--max));margin:0 auto;
  padding:56px 0 48px;
}
.hero h1,.page-hero h1,.article-header h1{
  font-size:clamp(1rem,1.6vw,1.25rem);
  font-weight:600;line-height:1.3;letter-spacing:-0.02em;
  color:var(--text);margin:0 0 14px;
}
.hero-text,.page-hero p,.article-header p{
  font-size:0.94rem;line-height:1.65;color:var(--text-2);max-width:48ch;
}
.hero-actions{display:flex;flex-wrap:wrap;gap:10px;margin:20px 0 18px}
.hero-meta{display:flex;flex-wrap:wrap;gap:7px;margin:0}
.hero-meta li{
  padding:4px 12px;border:1px solid var(--border);border-radius:999px;
  background:rgba(255,255,255,.5);color:var(--text-2);font-size:0.74rem;
}
.hero-panel{display:grid;gap:12px}
.glass-card{
  background:rgba(255,255,255,.8);border:1px solid var(--border);
  border-radius:var(--r-lg);padding:22px;
  box-shadow:var(--shadow-2);backdrop-filter:blur(10px);
}
.flow-list{
  padding-left:16px;list-style:decimal;
  color:var(--text-2);display:grid;gap:6px;font-size:0.84rem;
}
.metric-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}
.metric-card{
  padding:16px 14px;background:var(--white);
  border:1px solid var(--border);border-radius:var(--r);box-shadow:var(--shadow-1);
  display:grid;gap:2px;
}
.metric-card strong{
  font-size:1.7rem;font-weight:700;letter-spacing:-0.04em;color:var(--text);
  font-variant-numeric:tabular-nums;
}
.metric-card span{font-size:0.68rem;color:var(--text-2);line-height:1.3}

/* ── Sections ──────────────────────────────────────────────────── */
.section{
  padding:56px 0;
  width:min(calc(100% - 44px),var(--max));margin:0 auto;
}
.section-surface{
  width:100%;padding:56px max(22px,calc((100% - var(--max))/2 + 22px));
  background:var(--bg);border-top:1px solid var(--border);border-bottom:1px solid var(--border);
}
.section-heading{text-align:center;max-width:54ch;margin:0 auto 36px}
.section-heading h2{
  font-size:clamp(1.05rem,2vw,1.4rem);font-weight:600;
  letter-spacing:-0.025em;line-height:1.2;margin:0 0 10px;color:var(--text);
}
.section-text{color:var(--text-2);font-size:0.9rem;line-height:1.65;max-width:48ch;margin:0 auto}

/* ── Grids ─────────────────────────────────────────────────────── */
.feature-grid,.card-grid{
  display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px;
}
.feature-card,.content-card{
  padding:22px;background:var(--white);border:1px solid var(--border);
  border-radius:var(--r-lg);box-shadow:var(--shadow-1);
  transition:box-shadow 180ms,transform 180ms;
}
.feature-card:hover,.content-card:hover{box-shadow:var(--shadow-2);transform:translateY(-2px)}
.feature-card h3,.content-card h3,.step h3{
  font-size:0.9rem;font-weight:600;letter-spacing:-0.015em;margin:0 0 6px;
}
.feature-card p,.content-card p{
  font-size:0.84rem;color:var(--text-2);line-height:1.58;margin:0;
}
.text-link{
  display:inline-flex;align-items:center;gap:3px;
  margin-top:12px;font-size:0.82rem;font-weight:600;color:var(--green);
}
.text-link::after{content:" →"}

/* ── Split section ─────────────────────────────────────────────── */
.split-section{display:grid;grid-template-columns:1fr auto;gap:28px;align-items:center;padding:40px 0 32px}
.stack-card{
  display:grid;gap:7px;min-width:180px;
  background:var(--white);border:1px solid var(--border);
  border-radius:var(--r-lg);padding:20px;box-shadow:var(--shadow-1);
}
.stack-card span{
  padding:9px 13px;background:var(--bg);border:1px solid var(--border);
  border-radius:var(--r);font-size:0.82rem;color:var(--text-2);
}

/* ── Page inner ────────────────────────────────────────────────── */
.page-main{width:min(calc(100% - 44px),var(--max));margin:0 auto;padding-bottom:56px}
.page-main>.section{width:100%;margin:0}
.page-main>.section-surface{
  width:calc(100% + 44px);margin-left:-22px;
  padding:40px 22px;
}
.page-hero{padding:40px 0 28px}

/* ── TOC ───────────────────────────────────────────────────────── */
.toc-list{display:grid;gap:8px}
.toc-item,.toc-item-muted{
  display:grid;grid-template-columns:auto 1fr;gap:14px;align-items:center;
  padding:14px 18px;background:var(--white);border:1px solid var(--border);
  border-radius:var(--r);box-shadow:var(--shadow-1);
  transition:box-shadow 160ms,transform 160ms;
}
.toc-item:hover{box-shadow:var(--shadow-2);transform:translateY(-1px)}
.toc-item-muted{opacity:.5}
.toc-index{
  display:inline-grid;place-items:center;width:40px;height:40px;border-radius:10px;
  background:var(--green-light);color:var(--green);
  font-size:0.78rem;font-weight:700;letter-spacing:-0.01em;flex-shrink:0;
}
.toc-item strong{display:block;font-size:0.88rem;font-weight:600;letter-spacing:-0.01em}
.toc-item small{display:block;margin-top:2px;font-size:0.74rem;color:var(--text-2)}

/* ── Article ───────────────────────────────────────────────────── */
.article-layout{
  display:grid;grid-template-columns:210px minmax(0,1fr);gap:36px;align-items:start;
  width:min(calc(100% - 44px),var(--max));margin:0 auto;padding-bottom:56px;
}
.article-aside{position:sticky;top:calc(var(--nav) + 20px)}
.aside-card{
  display:grid;gap:8px;padding:18px;background:var(--white);
  border:1px solid var(--border);border-radius:var(--r-lg);box-shadow:var(--shadow-1);
}
.aside-card a,.aside-card p{font-size:0.78rem;color:var(--text-2);line-height:1.5}
.aside-card a:hover{color:var(--green)}
.article-header{padding:36px 0 20px;border-bottom:1px solid var(--border)}
.article-section{padding:24px 0;border-bottom:1px solid rgba(208,213,208,.6)}
.article-section h2{font-size:1.05rem;font-weight:600;letter-spacing:-0.02em;margin:0 0 10px}
.article-content p,.article-content li{font-size:0.9rem;color:var(--text-2);line-height:1.7}

/* ── Callout ───────────────────────────────────────────────────── */
.callout{margin-top:14px;padding:14px 18px;border-radius:var(--r);background:var(--white);border:1px solid var(--border);font-size:0.86rem}
.callout.soft{background:var(--green-light);border-color:var(--green-mid)}

/* ── Steps ─────────────────────────────────────────────────────── */
.steps{display:grid;gap:12px}
.step{display:grid;grid-template-columns:auto 1fr;gap:14px;align-items:start}
.step>span{
  display:inline-grid;place-items:center;width:32px;height:32px;
  border-radius:999px;background:var(--green-light);color:var(--green);
  font-size:0.78rem;font-weight:700;flex-shrink:0;
}
.bullet-list{padding-left:18px;list-style:disc}

/* ── Code ──────────────────────────────────────────────────────── */
.code-block{
  margin:12px 0 0;padding:14px 18px;overflow-x:auto;
  border:1px solid var(--border);border-radius:var(--r);
  background:#f8faf8;font-size:0.82rem;line-height:1.58;
}

/* ── Pager ─────────────────────────────────────────────────────── */
.pager{display:flex;justify-content:space-between;gap:14px;padding-top:24px}
.pager a{font-size:0.84rem;font-weight:600;color:var(--green)}

/* ── Footer ────────────────────────────────────────────────────── */
.site-footer{
  display:flex;justify-content:space-between;gap:12px;
  padding:18px max(22px,calc((100% - var(--max))/2 + 22px));
  border-top:1px solid var(--border);background:var(--bg);
  color:var(--text-2);font-size:0.74rem;
}

/* ── Figures ────────────────────────────────────────────────────── */
.article-figure{
  margin:28px 0;
  border:1px solid var(--border);
  border-radius:12px;
  overflow:hidden;
  background:#fff;
}
.article-figure img{
  display:block;
  width:100%;
  height:auto;
}
.article-figure figcaption{
  padding:10px 16px;
  font-size:0.78rem;
  color:var(--text-2);
  border-top:1px solid var(--border);
  line-height:1.5;
}
.article-figure--dark{background:#1e1e1e;border-color:#333}
.article-figure--dark figcaption{border-color:#333;color:#999}

/* ── Reveal ────────────────────────────────────────────────────── */
.reveal{opacity:0;transform:translateY(12px);transition:opacity 420ms ease,transform 420ms ease}
.reveal.is-visible{opacity:1;transform:translateY(0)}

/* ── Responsive ────────────────────────────────────────────────── */
@media(max-width:900px){
  .hero,.split-section{grid-template-columns:1fr}
  .hero{padding:36px 0 32px}
  .article-layout{grid-template-columns:1fr}
  .article-aside{position:static}
  .feature-grid,.card-grid{grid-template-columns:1fr 1fr}
  .metric-grid{grid-template-columns:repeat(3,1fr)}
}
@media(max-width:640px){
  .topbar{padding:0 18px;height:44px}
  .brand-copy span{display:none}
  .nav-toggle{display:inline-flex}
  .site-nav{
    display:none;position:absolute;top:100%;left:0;right:0;
    flex-direction:column;align-items:stretch;padding:10px 14px 14px;
    background:rgba(255,255,255,.96);border-bottom:1px solid var(--border);
    backdrop-filter:blur(20px);
  }
  .site-nav.is-open{display:flex}
  .site-nav a{padding:9px 12px;font-size:0.86rem}
  .feature-grid,.card-grid{grid-template-columns:1fr}
  .metric-grid{grid-template-columns:1fr}
  .section{padding:36px 0}
  .section-surface{padding:36px 18px}
  .section,.page-hero,.page-main,.article-layout{width:calc(100% - 32px)}
  .page-main>.section-surface{width:calc(100% + 32px);margin-left:-16px;padding:32px 16px}
  .pager,.site-footer{flex-direction:column}
  .site-footer{padding:16px 18px}
}