/* 数学ビジュアライズ — the site's own chrome (header, top page, series pages).
   Provisional plain white look: the real design comes later. The article components
   (theorems, proofs, figures, term cards) are in the shared /blog.css, which reads
   the tokens below. */

:root {
  --desk: #f4f5f8;
  --desk-2: #e9ebf1;
  --card: #ffffff;
  --ink: #15182b;
  --ink-2: #262a45;
  --soft: #5d627a;
  --faint: #8a8fa8;
  --line: rgba(21, 24, 43, .1);
  --line-strong: rgba(21, 24, 43, .22);
  --edu: #1f9d74;
  --dev: #3257ff;
  --ai: #ff6a3d;
  --edu-tint: #e3f4ee;
  --dev-tint: #e6ebff;
  --ai-tint: #ffece5;
  --night: #15182b;
  --night-text: #c9cce0;

  --font: "Zen Kaku Gothic New", "Hiragino Sans", "Noto Sans JP", sans-serif;
  --mono: "JetBrains Mono", ui-monospace, "SFMono-Regular", monospace;

  --gutter: clamp(16px, 4vw, 48px);
  --max: 1280px;
  --shadow: 0 0 0 1px var(--line);
  --shadow-lift: 0 0 0 1px var(--line-strong);
  --ease: cubic-bezier(.16, 1, .3, 1);
  --header-h: 0px;
}

*, *::before, *::after { box-sizing: border-box; }
html { background: var(--card); -webkit-text-size-adjust: 100%; }
body {
  margin: 0; background: var(--card); color: var(--ink);
  font-family: var(--font); font-size: 16px; line-height: 1.9;
  font-feature-settings: "palt" 1; -webkit-font-smoothing: antialiased; overflow-x: clip;
}
img { max-width: 100%; height: auto; display: block; }
a { color: inherit; }
button { font: inherit; color: inherit; }
:focus-visible { outline: 3px solid var(--dev); outline-offset: 3px; border-radius: 6px; }

.skip-link { position: absolute; left: 12px; top: -60px; z-index: 200; background: var(--ink); color: #fff; padding: 10px 16px; border-radius: 999px; font-weight: 700; text-decoration: none; }
.skip-link:focus { top: 12px; }
.wrap { width: 100%; max-width: var(--max); margin: 0 auto; padding: 0 var(--gutter); }

.display { font-weight: 900; line-height: 1.3; letter-spacing: -.01em; margin: 0; }
.h-lg { font-size: clamp(28px, 3.8vw, 52px); }
.lead { font-size: clamp(16px, 1.3vw, 18px); line-height: 2; margin: 0; max-width: 38em; color: var(--soft); }
.note { font-size: 13px; line-height: 1.9; color: var(--soft); margin: 0; }
.eyebrow { font-weight: 700; font-size: 13px; color: var(--soft); margin: 0; }
.text-link { display: inline-flex; align-items: center; gap: 6px; font-weight: 700; text-decoration: none; }
.text-link:hover { text-decoration: underline; }
.text-link svg, .btn-icon { width: 16px; height: 16px; }
.crumb { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; font-size: 13px; font-weight: 700; color: var(--soft); margin-bottom: 20px; }
.crumb a { text-decoration: none; }
.crumb a:hover { color: var(--ink); }
.section { padding: clamp(48px, 7vw, 96px) 0; }
.page-hero { padding: clamp(40px, 6vw, 88px) 0 clamp(32px, 5vw, 64px); }
.page-hero .lead { margin-top: 22px; }

/* ---------- Header and footer ---------- */
.mv-header { border-bottom: 1px solid var(--line); }
.mv-header .wrap { display: flex; align-items: center; justify-content: space-between; gap: 16px; min-height: 60px; }
.mv-logo { display: inline-flex; align-items: center; gap: 10px; font-weight: 900; font-size: 15px; letter-spacing: .04em; text-decoration: none; }
.mv-mark { width: 16px; height: 14px; flex: none; }
.mv-nav { display: flex; gap: 4px; }
.mv-nav a { padding: 6px 12px; border-radius: 8px; font-size: 14px; font-weight: 700; text-decoration: none; color: var(--soft); }
.mv-nav a:hover { color: var(--ink); background: var(--desk); }
.mv-footer { border-top: 1px solid var(--line); padding: 32px 0 40px; }
.mv-footer .wrap { display: grid; gap: 6px; }
.mv-footer p { margin: 0; }

/* ---------- Top page and series pages ---------- */
.mv-hero { padding: clamp(48px, 8vw, 112px) 0 clamp(32px, 5vw, 56px); }
.mv-hero .lead { margin-top: 20px; }
.mv-sections { display: grid; gap: clamp(48px, 6vw, 80px); padding-bottom: clamp(64px, 8vw, 112px); }
.mv-shelf { display: grid; gap: 20px; }
.mv-shelf + .mv-shelf { margin-top: clamp(48px, 6vw, 80px); }
.mv-shelf-head { display: grid; gap: 8px; max-width: 44em; }
.mv-shelf-head h2 { margin: 0; font-size: clamp(22px, 2.4vw, 30px); font-weight: 900; line-height: 1.4; }
.mv-shelf-head h2 a { text-decoration: none; }
.mv-shelf-head h2 a:hover { text-decoration: underline; }
.mv-list { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 340px), 1fr)); gap: 16px; }
.mv-item a { display: grid; gap: 8px; height: 100%; padding: 22px 24px; border-radius: 14px; box-shadow: 0 0 0 1px var(--line); text-decoration: none; transition: box-shadow .2s; }
.mv-item a:hover { box-shadow: 0 0 0 1px var(--line-strong); }
.mv-item p, .mv-item h3 { margin: 0; }
.mv-item-meta { font-size: 13px; font-weight: 700; color: var(--soft); }
.mv-item-title { font-size: 18px; font-weight: 900; line-height: 1.5; }
.mv-item-desc { font-size: 14px; line-height: 1.9; color: var(--soft); }