:root {
    --paper: #f6f4ee; --ink: #1d2420; --muted: #5c6660; --faint: #a8b0a9;
    --line: #dcdcd2; --tea: #33684d; --tea-soft: rgba(51, 104, 77, 0.13);
    --seal: #a63b2a; --card: #fcfbf7;
}
@media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) {
        --paper: #14181a; --ink: #e8e6dd; --muted: #9aa69e; --faint: #5c6660;
        --line: #2a322d; --tea: #6fae8b; --tea-soft: rgba(111, 174, 139, 0.18);
        --seal: #c9573f; --card: #191f1c;
    }
}
:root[data-theme="dark"] {
    --paper: #14181a; --ink: #e8e6dd; --muted: #9aa69e; --faint: #5c6660;
    --line: #2a322d; --tea: #6fae8b; --tea-soft: rgba(111, 174, 139, 0.18);
    --seal: #c9573f; --card: #191f1c;
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--paper); color: var(--ink); font: 17px/1.65 -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif; }
.page { max-width: 840px; margin: 0 auto; padding: 0 20px 80px; }
.mono { font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace; }
h1, h2, h3 { font-family: "Iowan Old Style", "Palatino Nova", Palatino, "Book Antiqua", Georgia, serif; font-weight: 600; }
h1 { font-size: 30px; margin: 10px 0 4px; }
h2 { font-size: 22px; margin: 36px 0 6px; }
h3 { font-size: 17px; margin: 18px 0 4px; }
nav.topnav { display: flex; gap: 14px; align-items: baseline; padding: 16px 0 8px; font-size: 13px; }
nav.topnav a { color: var(--muted); text-decoration: none; }
nav.topnav a[aria-current] { color: var(--ink); }
nav.topnav .spacer { flex: 1; }
.path { color: var(--muted); font-size: 12px; }
.path::before { content: "~/"; color: var(--faint); }
p.lede { color: var(--muted); margin: 0 0 18px; }
.pts { font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace; font-size: 12px; color: var(--tea); margin-left: 8px; }
.budget { font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace; font-size: 12px; color: var(--faint); }
.problem { background: var(--card); border: 1px solid var(--line); border-radius: 14px; padding: 18px 18px 14px; margin: 14px 0; }
.problem p { margin: 8px 0; }
.sub { margin: 14px 0 0; }
.sub .q { margin: 0 0 4px; }
.choices { color: var(--muted); font-size: 15px; margin: 2px 0 0 0; padding-left: 0; list-style: none; }
.choices li::before { content: "○ "; color: var(--faint); }
.bits { overflow-x: auto; margin: 10px 0 4px; padding-bottom: 4px; }
.bits table { border-collapse: collapse; font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace; }
.bits th { font-weight: 600; font-size: 12px; color: var(--muted); border: 1px solid var(--line); padding: 3px 0; text-align: center; }
.bits td { border: 1px solid var(--line); min-width: 22px; text-align: center; padding: 6px 0; font-size: 15px; }
.bits td.s { background: var(--tea-soft); }
.bits tr.idx td { font-size: 9px; color: var(--faint); padding: 1px 0; border-top: none; }
.caption { font-size: 13px; color: var(--muted); margin: 0 0 6px; }
.sol { border-left: 3px solid var(--tea); padding: 2px 0 2px 14px; margin: 10px 0 16px; }
.sol p { margin: 4px 0; }
.ans { font-weight: 600; }
a.btn { display: inline-block; margin-top: 18px; color: var(--tea); text-decoration: none; border-bottom: 1px solid var(--tea-soft); }
a.btn:hover { border-bottom-color: var(--tea); }
.cards { display: grid; gap: 12px; grid-template-columns: 1fr; }
@media (min-width: 620px) { .cards { grid-template-columns: 1fr 1fr; } }
a.tile { display: block; background: var(--card); border: 1px solid var(--line); border-radius: 14px; padding: 18px; color: inherit; text-decoration: none; }
a.tile:hover { border-color: var(--tea); }
a.tile h3 { margin: 0 0 4px; font-size: 18px; }
a.tile p { margin: 0; color: var(--muted); font-size: 15px; }
.tag { display: inline-block; font-size: 11px; color: var(--tea); background: var(--tea-soft); border-radius: 999px; padding: 2px 8px; margin-left: 6px; vertical-align: middle; }
footer { color: var(--faint); font-size: 12px; margin-top: 40px; }
@media (max-width: 620px) {
    .problem { padding: 14px 10px 12px; }
    .bits table { width: 100%; table-layout: fixed; }
    .bits td { min-width: 0; padding: 5px 0; font-size: 11px; }
    .bits th { font-size: 10px; }
    .bits tr.idx td { font-size: 6px; }
}