:root {
  --paper: #f4f1ea;
  --ink: #1b1916;
  --muted: #5c564c;
  --line: #d9d2c6;
  --card: #fbf9f4;
  --steel: #1e272c;
  --rust: #8f3d24;
  color: var(--ink);
  background: var(--paper);
  font-family: "Avenir Next", "Segoe UI", "Noto Sans CJK SC", sans-serif;
  font-size: 17px;
  line-height: 1.55;
}

* { box-sizing: border-box; }
body { margin: 0; }
a { color: var(--rust); }
img, svg { max-width: 100%; }

.bar, main, .foot {
  width: min(1040px, calc(100% - 32px));
  margin-inline: auto;
}

.bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 18px;
  padding: 22px 0 14px;
}

.mark {
  color: var(--ink);
  text-decoration: none;
  font-weight: 700;
  letter-spacing: 0.08em;
}

.nav { display: flex; gap: 18px; }
.nav a { color: var(--ink); text-decoration: none; }
.nav a[aria-current="page"] { border-bottom: 1px solid var(--ink); }

.hero, .block { padding: 28px 0; }
.hero { border-top: 2px solid var(--ink); }

.kicker, .label {
  color: var(--muted);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  font-size: 0.78rem;
}

h1, h2, h3 {
  font-family: Palatino, "Palatino Linotype", "Songti SC", serif;
  font-weight: 600;
  line-height: 1.15;
}

h1 { margin: 10px 0 12px; font-size: clamp(2.2rem, 5vw, 3.6rem); max-width: 16ch; }
h2 { margin: 0 0 12px; font-size: 1.8rem; }
.lead { max-width: 42rem; color: var(--muted); font-size: 1.08rem; }

.layout {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 28px;
  align-items: start;
}

.sheet, .card, form, .note {
  background: var(--card);
  border: 1px solid var(--line);
}

.diagram { padding: 16px; }
.diagram svg { display: block; width: 100%; height: auto; }
.caption { margin: 8px 0 0; color: var(--muted); font-size: 0.86rem; }

.series, .facts, .steps {
  display: grid;
  gap: 14px;
}
.series { grid-template-columns: repeat(3, 1fr); }
.facts { grid-template-columns: 1fr 1fr; }
.steps { grid-template-columns: repeat(3, 1fr); margin: 8px 0 0; padding: 0; list-style: none; }

.card, .note, form { padding: 16px 16px 18px; }
.card h3, .note h3 { margin: 8px 0; font-size: 1.25rem; }
.card p, .note p { margin: 0; color: var(--muted); }
.tag {
  display: inline-block;
  color: var(--steel);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

table { width: 100%; border-collapse: collapse; }
th, td { text-align: left; padding: 10px 8px; border-top: 1px solid var(--line); vertical-align: top; }
th { width: 34%; font-weight: 650; }

label { display: block; margin: 0 0 12px; font-size: 0.92rem; }
input, textarea, select {
  display: block;
  width: 100%;
  margin-top: 6px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  font: inherit;
}
textarea { min-height: 120px; resize: vertical; }
.pair { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.trap { position: absolute; left: -9999px; height: 0; overflow: hidden; }

button, .button {
  display: inline-block;
  border: 0;
  background: var(--steel);
  color: #f7f4ee;
  text-decoration: none;
  font: inherit;
  letter-spacing: 0.08em;
  padding: 11px 18px;
  cursor: pointer;
}
button:disabled { opacity: 0.6; cursor: wait; }
.status { min-height: 1.4em; color: var(--steel); }
.status[data-kind="error"] { color: var(--rust); }

.foot {
  border-top: 1px solid var(--line);
  padding: 18px 0 36px;
  color: var(--muted);
  font-size: 0.92rem;
}
.foot p { margin: 0 0 4px; }

@media (max-width: 800px) {
  .layout, .series, .facts, .steps, .pair, .nav { display: block; }
  .nav a { display: inline-block; margin: 8px 14px 0 0; }
  .card, .note { margin-top: 12px; }
}