:root {
  --bg: #fbfaf7;
  --surface: #f2f0ea;
  --text: #1b1b19;
  --text-2: #55534e;
  --text-3: #8a8780;
  --line: #dedbd2;
  --accent: #2a6fc9;
  --accent-soft: #e4eefb;
  --ok: #1f8a4c;
  --plot: #2a78d6;
  --plot-ref: #8a8780;
  --plot-axis: #c3c2b7;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #161615;
    --surface: #212120;
    --text: #efeee9;
    --text-2: #c0beb4;
    --text-3: #8a8780;
    --line: #333331;
    --accent: #6ea8f2;
    --accent-soft: #1d2b3f;
    --ok: #55c486;
    --plot: #3987e5;
    --plot-ref: #8a8780;
    --plot-axis: #3a3a37;
  }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Pretendard", "Apple SD Gothic Neo", "Malgun Gothic", system-ui, sans-serif;
  font-size: 17px;
  line-height: 1.75;
  word-break: keep-all;
}
.wrap { max-width: 780px; margin: 0 auto; padding: 0 20px 80px; }
header.site {
  border-bottom: 1px solid var(--line);
  margin-bottom: 40px;
}
header.site .wrap { padding-top: 18px; padding-bottom: 18px; display: flex; gap: 20px; align-items: baseline; flex-wrap: wrap; }
header.site a.brand { font-weight: 700; color: var(--text); text-decoration: none; }
header.site nav a { color: var(--text-2); text-decoration: none; margin-right: 16px; font-size: 15px; }
header.site nav a:hover { color: var(--accent); }
h1 { font-size: 32px; line-height: 1.3; margin: 0 0 8px; letter-spacing: -0.01em; }
h2 { font-size: 23px; line-height: 1.4; margin: 56px 0 12px; }
h3 { font-size: 18px; margin: 32px 0 8px; }
p { margin: 0 0 16px; }
.lead { color: var(--text-2); font-size: 18px; margin-bottom: 28px; }
.crumb { font-size: 14px; color: var(--text-3); margin-bottom: 12px; }
.crumb a { color: var(--text-3); }
a { color: var(--accent); }
code {
  font-family: "Cascadia Code", Consolas, "D2Coding", monospace;
  font-size: 0.9em;
  background: var(--surface);
  padding: 1px 6px;
  border-radius: 4px;
}
.formula {
  background: var(--surface);
  border-radius: 8px;
  padding: 14px 18px;
  margin: 0 0 16px;
  font-family: "Cascadia Code", Consolas, "D2Coding", monospace;
  font-size: 16px;
  overflow-x: auto;
  white-space: nowrap;
}
.note {
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  padding: 12px 16px;
  margin: 0 0 16px;
}
.note p:last-child { margin-bottom: 0; }
.q {
  margin: 40px 0 16px;
  padding: 12px 16px;
  background: var(--surface);
  border-radius: 8px;
  font-weight: 600;
}
.q .who { display: block; font-size: 13px; font-weight: 400; color: var(--text-3); margin-bottom: 2px; }
.table-scroll { overflow-x: auto; margin: 0 0 20px; }
table { border-collapse: collapse; width: 100%; font-size: 15.5px; line-height: 1.6; }
th, td { text-align: left; vertical-align: top; padding: 10px 12px; border-bottom: 1px solid var(--line); }
th { font-weight: 600; color: var(--text-2); font-size: 14px; white-space: nowrap; }
td.num { white-space: nowrap; color: var(--text-3); }
.tag {
  display: inline-block;
  font-size: 12.5px;
  padding: 1px 8px;
  border-radius: 999px;
  border: 1px solid var(--line);
  color: var(--text-3);
  white-space: nowrap;
}
.tag.now { border-color: var(--accent); color: var(--accent); }
.tag.done { border-color: var(--ok); color: var(--ok); }
ul.lessons { list-style: none; padding: 0; margin: 0 0 20px; }
ul.lessons li { margin: 0; padding: 10px 0; border-bottom: 1px solid var(--line); display: flex; gap: 12px; align-items: baseline; flex-wrap: wrap; }
ul.lessons li .n { color: var(--text-3); min-width: 34px; font-variant-numeric: tabular-nums; }
ul.lessons li .t { flex: 1; min-width: 200px; }
.demo {
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 18px;
  margin: 20px 0 24px;
}
.demo .row { display: flex; align-items: center; gap: 12px; margin-bottom: 14px; }
.demo .row label { font-size: 14.5px; color: var(--text-2); white-space: nowrap; }
.demo .row input[type=range] { flex: 1; min-width: 0; accent-color: var(--accent); }
.demo .row output { font-weight: 600; min-width: 40px; text-align: right; font-variant-numeric: tabular-nums; }
.demo .stats { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 10px; margin-bottom: 14px; }
.demo .stat { background: var(--surface); border-radius: 8px; padding: 10px 14px; }
.demo .stat .k { font-size: 13px; color: var(--text-2); }
.demo .stat .v { font-size: 22px; font-weight: 600; font-variant-numeric: tabular-nums; }
.demo .legend { display: flex; flex-wrap: wrap; gap: 14px; font-size: 13px; color: var(--text-2); margin-bottom: 8px; }
.demo .legend span { display: inline-flex; align-items: center; gap: 6px; }
.demo .legend i.box { width: 10px; height: 10px; border-radius: 2px; background: var(--plot); display: inline-block; }
.demo .legend i.line { width: 18px; border-top: 2px solid var(--plot); display: inline-block; }
.demo .legend i.dash { width: 18px; border-top: 2px dashed var(--plot-ref); display: inline-block; }
.demo .plot { position: relative; width: 100%; height: 340px; }
.demo canvas { display: block; }
.demo .buttons { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 12px; }
button {
  font: inherit;
  font-size: 14.5px;
  padding: 6px 14px;
  border-radius: 8px;
  border: 1px solid var(--line);
  background: transparent;
  color: var(--text);
  cursor: pointer;
}
button:hover { background: var(--surface); }
ul.lessons li .desc { color: var(--text-2); font-size: 15px; }
ol li, ul li { margin-bottom: 6px; }
.pager { display: flex; justify-content: space-between; gap: 16px; flex-wrap: wrap; margin-top: 56px; font-size: 15px; }
.pager .next { color: var(--text-3); }
.fine { font-size: 13.5px; color: var(--text-3); margin-top: 40px; }