:root {
  --bg: #fbfbf9;
  --surface: #ffffff;
  --text: #1f2328;
  --muted: #5f6670;
  --line: #e3e3de;
  --accent: #1f5f8b;
  --tag-bg: #eef3f7;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #15171a;
    --surface: #1c1f23;
    --text: #e6e7e9;
    --muted: #9aa1aa;
    --line: #2c3036;
    --accent: #7db7e0;
    --tag-bg: #232a31;
    color-scheme: dark;
  }
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 4.5rem; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Hiragino Sans", "Hiragino Kaku Gothic ProN",
    "Noto Sans JP", "Segoe UI", Meiryo, sans-serif;
  font-size: 16px;
  line-height: 1.75;
  -webkit-text-size-adjust: 100%;
}

/* Language switching: only the active language's spans are shown. */
html[data-lang="ja"] .en,
html[data-lang="en"] .ja { display: none !important; }

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.wrap { max-width: 780px; margin: 0 auto; padding: 0 16px; }

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: color-mix(in srgb, var(--bg) 90%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}

.header-inner {
  display: flex;
  align-items: center;
  gap: 1rem;
  height: 3.5rem;
}

.brand { color: var(--text); font-weight: 600; white-space: nowrap; }

.nav { display: flex; gap: 1rem; margin-left: auto; font-size: 0.92rem; }
.nav a { color: var(--muted); }
.nav a:hover { color: var(--text); text-decoration: none; }

.lang-toggle {
  font: inherit;
  font-size: 0.85rem;
  color: var(--text);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 0.2rem 0.8rem;
  cursor: pointer;
}
.lang-toggle:hover { border-color: var(--accent); }

.hero { padding: 3.5rem 0 1rem; }
.hero h1 { font-size: 2.2rem; line-height: 1.3; margin: 0; letter-spacing: 0.02em; }
.hero .sub { color: var(--muted); margin: 0.4rem 0 0; }
.hero .links { display: flex; gap: 1.2rem; margin: 1rem 0 0; }

section { padding: 1.5rem 0; }
section + section { border-top: 1px solid var(--line); }

h2 { font-size: 1.4rem; margin: 1rem 0 0.8rem; }
h3 { font-size: 1rem; color: var(--muted); font-weight: 600; margin: 1.6rem 0 0.5rem; }

.timeline { list-style: none; padding: 0; margin: 0; }
.timeline > li { display: flex; gap: 1rem; }
.timeline > li + li { margin-top: 1.2rem; }
.timeline .when { flex: 0 0 3.5rem; color: var(--muted); font-variant-numeric: tabular-nums; }
.timeline .what { flex: 1; min-width: 0; }
.timeline .org { display: block; font-weight: 600; }
.timeline .desc { display: block; color: var(--muted); font-size: 0.92rem; margin: 0.15rem 0 0; }

.themes { list-style: none; padding: 0; margin: 0.9rem 0 0; }
.themes > li { padding: 0.7rem 0; border-top: 1px solid var(--line); font-size: 0.92rem; }
.themes strong { display: block; font-size: 1rem; font-weight: 600; }
.nums { display: flex; flex-wrap: wrap; gap: 0.2rem 1rem; align-items: center; font-size: 0.85rem; margin-top: 0.15rem; }

.count { color: var(--muted); font-size: 0.85rem; font-weight: 400; margin-left: 0.3rem; }

.tags { list-style: none; padding: 0; margin: 1rem 0 0; display: flex; flex-wrap: wrap; gap: 0.5rem; }
.tags li { background: var(--tag-bg); border-radius: 999px; padding: 0.1rem 0.8rem; font-size: 0.9rem; }

.refs { padding-left: 1.4rem; margin: 0; }
.refs li { margin: 0 0 0.9rem; padding-left: 0.2rem; }
.refs b { font-weight: 600; }
.refs .id { font-size: 0.85rem; margin-left: 0.3rem; white-space: nowrap; }

.note { color: var(--muted); font-size: 0.9rem; margin: 0 0 1rem; }

.patents .meta { color: var(--muted); font-size: 0.88rem; }
.patents .status {
  font-size: 0.75rem;
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 0 0.4rem;
  color: var(--muted);
}

.site-footer { border-top: 1px solid var(--line); color: var(--muted); font-size: 0.85rem; padding: 1.5rem 0 2.5rem; }

@media (max-width: 560px) {
  .nav { display: none; }
  .lang-toggle { margin-left: auto; }
  .hero { padding-top: 2.5rem; }
  .hero h1 { font-size: 1.8rem; }
  .timeline > li { flex-direction: column; gap: 0; }
  .timeline .when { flex: none; }
}