:root {
  --bg: #ffffff; --text: #1d2329; --muted: #5b6670; --line: #d7dde2;
  --accent: #1f5f8b; --accent-text: #ffffff; --solved: #e6f2ea; --solved-line: #2e7d4f;
  --err: #a8322d;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #15191d; --text: #e8ecef; --muted: #9aa5ae; --line: #343c44;
    --accent: #5aa3d6; --accent-text: #0d1114; --solved: #1d3326; --solved-line: #5cc285;
    --err: #ff8a80;
  }
}
* { box-sizing: border-box; }
body {
  margin: 0; background: var(--bg); color: var(--text);
  font: 16px/1.5 system-ui, -apple-system, "Segoe UI", Roboto, Arial, sans-serif;
}
main { max-width: 720px; margin: 0 auto; padding: 24px 16px 48px; }
h1 { font-size: 1.6rem; margin: 8px 0 4px; }
h2 { font-size: 1.1rem; margin: 28px 0 8px; color: var(--muted); }
a { color: var(--accent); }
.back { font-size: 0.9rem; }
.eq {
  font-family: "Cambria Math", "STIX Two Math", Georgia, serif; font-size: 1.15rem;
  padding: 12px 14px; border: 1px solid var(--line); border-radius: 8px; overflow-x: auto;
}
.how { color: var(--muted); font-size: 0.95rem; }
.row {
  display: grid; grid-template-columns: 1fr 140px; grid-template-areas: "name name" "input unit";
  gap: 4px 10px; align-items: center; padding: 10px 0; border-bottom: 1px solid var(--line);
}
.row .name { grid-area: name; }
.row input { grid-area: input; }
.row .unit { grid-area: unit; color: var(--muted); font-size: 0.9rem; }
input {
  width: 100%; font: inherit; padding: 8px 10px; color: var(--text); background: var(--bg);
  border: 1px solid var(--line); border-radius: 6px;
}
input:focus { outline: 2px solid var(--accent); outline-offset: 1px; }
input.solved { background: var(--solved); border-color: var(--solved-line); font-weight: 600; }
.buttons { display: flex; gap: 10px; margin-top: 18px; }
button {
  font: inherit; font-weight: 600; padding: 10px 22px; border-radius: 6px; cursor: pointer;
  border: 1px solid var(--accent); background: var(--accent); color: var(--accent-text);
}
button.secondary { background: transparent; color: var(--accent); }
#msg { min-height: 1.5em; margin-top: 14px; font-weight: 600; }
#msg.err { color: var(--err); }
.src, .disclaimer { color: var(--muted); font-size: 0.85rem; }
.disclaimer { margin-top: 32px; border-top: 1px solid var(--line); padding-top: 12px; }
ul.list { list-style: none; padding: 0; margin: 0; }
ul.list li { padding: 8px 0; border-bottom: 1px solid var(--line); }
@media (min-width: 560px) {
  .row { grid-template-columns: 1fr 160px 150px; grid-template-areas: "name input unit"; }
}