/* 1. Variables (14-color-backgrounds: CSS variables) */:root {
  --bg: #fff;
  --fg: #111;
  --muted: #666;
  --line: #ddd;
  --accent: #0b57d0;
  --accent-2: #14522a;
  --paper: #fafafa;
  --radius: 12px;
  --radius-pill: 999px;
  --max: 860px;
  --font-sans: -apple-system, Helvetica, Arial, sans-serif;
  --font-serif: Georgia, 'Times New Roman', serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
}

/* 2. Reset (06-box-model) */
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font-serif);
  font-size: 16px;
  line-height: 1.6;
  color: var(--fg);
  background: var(--bg);
}

/* 3. Base typography (13-typography) */
h1, h2, h3 { font-family: var(--font-sans); line-height: 1.25; color: #000; }
h1 { font-size: clamp(1.9rem, 4vw, 2.6rem); margin: 8px 0 10px; }
h2 { font-size: 20px; margin: 0 0 8px; }
h3 { font-size: 14px; margin: 10px 0 4px; text-transform: none; letter-spacing: 0; }
p { margin: 0 0 10px; }
a { color: var(--accent); text-underline-offset: 2px; }
a:hover { color: #052e6e; }
a:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 2px; }
code { font-family: var(--font-mono); font-size: 0.85em; background: #f4f4f4; padding: 1px 4px; border-radius: 3px; }
table { border-collapse: collapse; width: 100%; font-family: var(--font-sans); font-size: 13px; margin: 10px 0; }
th, td { text-align: left; padding: 6px 8px; border: 1px solid var(--line); }
th { background: var(--paper); font-size: 11px; text-transform: uppercase; letter-spacing: 0.05em; }
ul, ol { padding-left: 20px; }
hr { border: none; border-top: 1px solid var(--line); margin: 24px 0; }

/* Shared containers */
.site-header, main, .site-footer > .footer__grid {
  max-width: var(--max);
  margin: 0 auto;
  padding-left: 16px;
  padding-right: 16px;
}

/* 4. Components */

/* Header — flexbox (09) */
.site-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  padding-top: 14px;
  padding-bottom: 14px;
  border-bottom: 1px solid var(--line);
  position: sticky; /* 11-position */
  top: 0;
  background: #fff;
  z-index: 10;
}
.logo {
  font-family: var(--font-sans);
  font-weight: 800;
  font-size: 18px;
  letter-spacing: -0.02em;
  color: var(--fg);
  text-decoration: none;
  border: 1.5px solid var(--fg);
  padding: 4px 10px;
  border-radius: 6px;
}
.logo:hover { background: var(--fg); color: #fff; }
.site-nav ul {
  display: flex;
  gap: 16px;
  align-items: center;
  list-style: none;
  margin: 0;
  padding: 0;
  font-family: var(--font-sans);
  font-size: 14px;
}
.site-nav a { text-decoration: none; color: var(--muted); }
.site-nav a:hover { color: var(--fg); text-decoration: underline; }
.nav-cta {
  background: var(--fg);
  color: #fff !important;
  padding: 6px 12px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--fg);
  transition: transform 180ms ease, box-shadow 180ms ease, background 180ms ease; /* 16-transitions */
}
.nav-cta:hover { transform: translateY(-1px); box-shadow: 0 4px 12px rgba(0,0,0,0.12); background: #222; text-decoration: none !important; }

/* Hero — grid + flex (10, 09) */
.hero {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 28px;
  padding: 28px 0 20px;
  align-items: start;
}
.eyebrow {
  font-family: var(--font-sans);
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: #888;
  margin: 0;
}
.hero h1 span { color: var(--accent); }
.lead { color: #444; font-size: 17px; line-height: 1.5; max-width: 36em; }
.hero__actions { display: flex; gap: 10px; flex-wrap: wrap; margin: 14px 0 16px; }
.btn {
  font-family: var(--font-sans);
  font-size: 14px;
  font-weight: 600;
  padding: 10px 16px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--fg);
  text-decoration: none;
  display: inline-block;
  cursor: pointer;
  transition: transform 180ms ease, box-shadow 180ms ease, background 180ms ease, color 180ms ease; /* 16 */
}
.btn:hover { transform: translateY(-2px); box-shadow: 0 6px 16px rgba(0,0,0,0.12); }
.btn--primary { background: var(--fg); color: #fff; }
.btn--primary:hover { background: #222; color: #fff; }
.btn--ghost { background: #fff; color: var(--fg); }
.btn--ghost:hover { background: var(--paper); }
.btn--block { width: 100%; text-align: center; }
.hero__meta {
  list-style: none;
  padding: 0;
  margin: 8px 0 0;
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  font-family: var(--font-sans);
  font-size: 12px;
  color: var(--muted);
  border-top: 1px solid #eee;
  padding-top: 12px;
}
.hero__meta strong { color: var(--fg); }

/* Decorative stack — position + grid centering (07, 11) */
.hero__art { display: grid; gap: 10px; }
.stack {
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: var(--radius);
  padding: 18px;
  display: grid;
  gap: 8px;
  position: relative;
  overflow: hidden;
}
.stack::before {
  content: "";
  position: absolute;
  inset: auto -20% -30% -20%;
  height: 55%;
  background: radial-gradient(ellipse at center, rgba(11,87,208,0.08), transparent 70%);
  pointer-events: none;
}
.stack__book {
  border: 1px solid var(--fg);
  background: #fff;
  border-radius: 6px;
  padding: 12px 14px;
  font-family: var(--font-sans);
  font-size: 13px;
  font-weight: 700;
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: relative;
  transition: transform 180ms ease, box-shadow 180ms ease;
}
.stack__book:hover { transform: translateX(4px); box-shadow: 0 4px 10px rgba(0,0,0,0.08); }
.stack__book::after { content: "—  " attr(data-price); font-weight: 400; color: var(--muted); font-size: 12px; }
.stack__book--1 { transform: rotate(-0.6deg); }
.stack__book--2 { transform: rotate(0.5deg); margin-left: 6px; }
.stack__book--3 { transform: rotate(-0.4deg); }
.stack__book--4 { transform: rotate(0.3deg); margin-left: 4px; }
.hero__caption { font-family: var(--font-sans); font-size: 12px; color: #888; text-align: center; margin: 0; }

/* Sections */
.section { padding: 22px 0; border-top: 1px solid #eee; }
.section__head { max-width: 40em; margin-bottom: 14px; }
.section__head p { color: var(--muted); font-family: var(--font-sans); font-size: 14px; }
.section--narrow { max-width: 36em; }
.section--split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
  align-items: start;
}
.shop-figure { margin: 0; }
.shop-figure img {
  width: 100%;
  height: auto;
  display: block;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
}
.shop-figure figcaption {
  font-family: var(--font-sans);
  font-size: 12px;
  color: #888;
  margin-top: 6px;
  text-align: center;
}
blockquote {
  margin: 14px 0 0;
  padding: 10px 14px;
  border-left: 3px solid var(--line);
  background: var(--paper);
  font-size: 14px;
  color: #333;
}
blockquote cite { display: block; margin-top: 6px; font-size: 12px; color: var(--muted); font-style: normal; }
details {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 14px;
  background: var(--paper);
  font-family: var(--font-sans);
  font-size: 14px;
  margin-top: 14px;
}
details summary { cursor: pointer; font-weight: 600; }
details[open] summary { margin-bottom: 8px; }

/* Book grid — auto-fit (12-responsive, 10-grid) */
.book-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 14px;
}
.card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
  padding: 14px;
  display: flex;
  flex-direction: column;
  gap: 6px;
  transition: transform 180ms ease, box-shadow 180ms ease, border-color 180ms ease; /* 16 */
}
.card:hover { transform: translateY(-4px); box-shadow: 0 8px 20px rgba(0,0,0,0.08); border-color: #bbb; }
.card__cover {
  height: 86px;
  border-radius: 8px;
  display: grid;
  place-items: center; /* 07-center */
  font-size: 28px;
  border: 1px solid rgba(0,0,0,0.06);
  margin-bottom: 4px;
}
.card__title { font-size: 15px; margin: 0; }
.card__author { font-family: var(--font-sans); font-size: 12px; color: var(--muted); margin: 0; }
.card__desc { font-size: 13px; color: #333; line-height: 1.5; margin: 4px 0 2px; }
.card__meta { margin-top: auto; font-size: 12px; }
.badge {
  display: inline-block;
  align-self: flex-start;
  font-family: var(--font-sans);
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  padding: 3px 7px;
  border-radius: var(--radius-pill);
  background: #daf5df;
  border: 1px solid #8fd19b;
  color: var(--accent-2);
}
.card--featured { border-color: #8fd19b; background: #fbfffc; }

/* Form — module 15 */
.section--form { display: grid; place-items: center; background: var(--paper); border-radius: var(--radius); border: 1px solid var(--line); margin-top: 10px; }
.form-card {
  width: 100%;
  max-width: 520px;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: 0 4px 16px rgba(0,0,0,0.04);
}
.form-card h2 { margin-top: 0; }
.form-card > p { color: var(--muted); font-family: var(--font-sans); font-size: 14px; }
form { display: grid; gap: 12px; margin-top: 12px; }
.field { display: grid; gap: 6px; }
.field label, fieldset legend {
  font-family: var(--font-sans);
  font-size: 13px;
  font-weight: 600;
}
fieldset { border: 1px solid var(--line); border-radius: 8px; padding: 10px 12px; margin: 0; }
.choice { font-weight: 400; display: flex; gap: 8px; align-items: center; cursor: pointer; font-size: 14px; font-family: var(--font-sans); }
input[type="text"], input[type="email"], select {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid #bbb;
  border-radius: 8px;
  font-family: var(--font-sans);
  font-size: 14px;
  background: #fff;
  transition: border-color 150ms ease, box-shadow 150ms ease;
}
input:hover, select:hover { border-color: #888; }
input:focus, select:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 3px rgba(11,87,208,0.15); }
input:focus-visible, select:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
input:invalid:not(:placeholder-shown) { border-color: #d00; background: #fff5f5; }
select { cursor: pointer; }
.form__hint { font-family: var(--font-sans); font-size: 12px; color: #888; margin: 0; text-align: center; }
button[type="submit"]:hover { transform: translateY(-1px); }

/* Footer — grid */
.site-footer {
  margin-top: 28px;
  border-top: 1px solid var(--line);
  background: var(--paper);
  padding: 18px 0 28px;
  font-family: var(--font-sans);
  font-size: 13px;
  color: var(--muted);
}
.footer__grid {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 16px;
  align-items: start;
}
.footer__grid ul { list-style: none; padding: 0; margin: 0; display: flex; gap: 12px; flex-wrap: wrap; }
.footer__grid a { color: var(--muted); }
.footer__grid a:hover { color: var(--fg); }
.footer__note { grid-column: 1 / -1; border-top: 1px solid #eee; padding-top: 12px; margin-top: 4px; font-size: 12px; }
.footer__note a { color: var(--accent); }

/* 5. Responsive — 12-responsive: one breakpoint + free responsiveness from auto-fit/wrap/clamp */
@media (max-width: 700px) {
  .hero { grid-template-columns: 1fr; }
  .section--split { grid-template-columns: 1fr; }
  .footer__grid { grid-template-columns: 1fr; }
  .site-header { flex-wrap: wrap; }
  .site-nav ul { gap: 10px; font-size: 13px; }
}

/* Reduced motion (16) */
@media (prefers-reduced-motion: reduce) {
  * { scroll-behavior: auto !important; transition: none !important; }
}