:root {
  --bg: #FAFAF7;
  --surface: #FFFFFF;
  --ink: #15171C;
  --ink-2: #3E434C;
  --muted: #555B66;
  --line: #E4E4DE;
  --chip: #F2F2EE;
  --accent: #1D4ED8;
  --accent-ink: #1E3A8A;
  --accent-soft: #EAF0FD;
  --mono: "IBM Plex Mono", ui-monospace, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #111317;
    --surface: #1A1D23;
    --ink: #ECEDEF;
    --ink-2: #C4C8CF;
    --muted: #9AA0AA;
    --line: #2C3038;
    --chip: #252930;
    --accent: #6B93F5;
    --accent-ink: #A9C1FA;
    --accent-soft: #1C2742;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: Inter, system-ui, sans-serif;
  line-height: 1.5;
}

a { color: var(--accent); }

.wrap { max-width: 1120px; margin: 0 auto; padding: 0 16px; }
.muted { color: var(--muted); }

/* Header */
.site-header { background: var(--surface); border-bottom: 1px solid var(--line); }
.header-row { display: flex; flex-wrap: wrap; align-items: center; gap: 12px 28px; padding-top: 14px; padding-bottom: 14px; }
.logo { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--ink); font-weight: 700; font-size: 19px; }
.logo svg { color: var(--accent); }
nav a { color: var(--muted); text-decoration: none; font-weight: 500; padding: 10px 0; }
nav a[aria-current="page"] { color: var(--ink); border-bottom: 2px solid var(--accent); }

/* Intro */
.page { padding-top: 48px; padding-bottom: 80px; display: flex; flex-direction: column; gap: 32px; }
.intro { display: flex; flex-wrap: wrap; gap: 24px; align-items: flex-start; }
.intro-text { flex: 999 1 480px; display: flex; flex-direction: column; gap: 12px; }
h1 { margin: 0; font-size: clamp(30px, 4.5vw, 44px); letter-spacing: -0.02em; line-height: 1.1; }
.lead { margin: 0; font-size: 18px; line-height: 1.55; color: var(--ink-2); }

.search { display: flex; flex-direction: column; gap: 6px; padding-top: 8px; font-size: 14px; font-weight: 600; }
.search input {
  font: inherit; font-size: 16px; font-weight: 400;
  padding: 12px 14px; max-width: 420px;
  border: 1px solid var(--line); border-radius: 10px;
  background: var(--surface); color: var(--ink);
}
.search input:focus { outline: 2px solid var(--accent); outline-offset: 1px; }

.example-co {
  flex: 1 1 300px; background: var(--surface); border: 1px solid var(--line);
  border-radius: 14px; padding: 20px; display: flex; flex-direction: column; gap: 10px; font-size: 14px;
}
.example-co strong { font-size: 15px; }
.example-co dl { margin: 0; display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 6px 16px; font-size: 13px; }
.example-co dt { color: var(--muted); }
.example-co dd { margin: 0; font-family: var(--mono); }

/* Groups */
#groups { display: flex; flex-direction: column; gap: 40px; }
.group { display: flex; flex-direction: column; gap: 14px; }
.group-head { display: flex; flex-wrap: wrap; align-items: baseline; gap: 6px 14px; border-bottom: 1px solid var(--line); padding-bottom: 10px; }
.group-head h2 { margin: 0; font-size: 22px; }
.tag {
  font-size: 12px; font-weight: 600; letter-spacing: 0.04em; text-transform: uppercase;
  padding: 4px 10px; border-radius: 999px; background: var(--chip); color: var(--ink-2);
}
.tag.step { background: var(--accent); color: #FFFFFF; }
.count { font-size: 14px; color: var(--muted); }

.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(320px, 100%), 1fr)); gap: 10px; }

.term {
  background: var(--surface); border: 1px solid var(--line); border-radius: 12px;
  padding: 16px; display: flex; flex-direction: column; gap: 8px; scroll-margin-top: 16px;
}
.term:target { border-color: var(--accent); box-shadow: 0 0 0 2px var(--accent-soft); }
.term h3 { margin: 0; font-size: 16px; }
.term p { margin: 0; font-size: 14px; line-height: 1.5; color: var(--ink-2); }
.math { display: flex; flex-direction: column; gap: 4px; background: var(--accent-soft); padding: 8px 10px; border-radius: 8px; font-family: var(--mono); font-size: 13px; }
.math .formula { color: var(--accent-ink); }
.math .example { color: var(--ink); }

/* Footer */
.site-footer { border-top: 1px solid var(--line); background: var(--surface); }
.site-footer .wrap { padding-top: 28px; padding-bottom: 28px; font-size: 14px; color: var(--muted); }