:root {
  --bg: #f6f5f1;
  --card: #ffffff;
  --ink: #1d1d1f;
  --muted: #6b6b70;
  --line: #e4e2dc;
  --accent: #c5050c; /* UW red */
  --graphs: #2f6fdf;
  --shortest: #7b3fd1;
  --mst: #138a5b;
  --greedy: #d07a00;
  --flow: #0b8fa8;
  --concepts: #555;
  --radius: 12px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: "Segoe UI", system-ui, -apple-system, Roboto, sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.55;
}

header.top {
  background: #1d1d1f;
  color: #fff;
  padding: 28px 24px 22px;
}

header.top .wrap { max-width: 1100px; margin: 0 auto; }

header.top h1 { margin: 0 0 4px; font-size: 1.8rem; letter-spacing: -0.01em; }
header.top h1 span { color: #ff5a5f; }
header.top p { margin: 0; color: #c9c9cf; }

.stats {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 16px;
}

.stat {
  background: #2b2b2f;
  border-radius: 10px;
  padding: 8px 14px;
  font-size: 0.9rem;
}
.stat b { font-size: 1.15rem; margin-right: 4px; color: #fff; }

.progress {
  height: 6px;
  background: #2b2b2f;
  border-radius: 99px;
  margin-top: 14px;
  overflow: hidden;
}
.progress > div {
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, #ff5a5f, #ffb347);
  transition: width 0.3s;
}

.toolbar {
  position: sticky;
  top: 0;
  z-index: 10;
  background: rgba(246, 245, 241, 0.95);
  backdrop-filter: blur(6px);
  border-bottom: 1px solid var(--line);
}
.toolbar .wrap {
  max-width: 1100px;
  margin: 0 auto;
  padding: 12px 24px;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
}

.chips { display: flex; flex-wrap: wrap; gap: 6px; }

.chip {
  border: 1px solid var(--line);
  background: #fff;
  border-radius: 99px;
  padding: 5px 12px;
  font-size: 0.85rem;
  cursor: pointer;
  color: var(--ink);
}
.chip:hover { border-color: #bbb; }
.chip.active { background: var(--ink); color: #fff; border-color: var(--ink); }
.chip .count { opacity: 0.6; margin-left: 4px; font-size: 0.78rem; }

.toolbar input[type="search"], .toolbar select {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 6px 10px;
  font: inherit;
  font-size: 0.9rem;
  background: #fff;
}
.toolbar input[type="search"] { flex: 1; min-width: 180px; }

.toolbar label.toggle { font-size: 0.85rem; color: var(--muted); display: flex; gap: 6px; align-items: center; }

.btn {
  border: 1px solid var(--ink);
  background: var(--ink);
  color: #fff;
  border-radius: 8px;
  padding: 6px 12px;
  font: inherit;
  font-size: 0.85rem;
  cursor: pointer;
}
.btn.ghost { background: #fff; color: var(--ink); }

main { max-width: 1100px; margin: 0 auto; padding: 20px 24px 80px; }

.section-title {
  margin: 34px 0 6px;
  font-size: 1.25rem;
  display: flex;
  align-items: center;
  gap: 10px;
}
.section-title::before {
  content: "";
  width: 10px;
  height: 22px;
  border-radius: 3px;
  background: var(--c, var(--ink));
}
.section-desc { margin: 0 0 14px; color: var(--muted); font-size: 0.92rem; }

.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-left: 5px solid var(--c, var(--ink));
  border-radius: var(--radius);
  padding: 16px 20px 12px;
  margin: 12px 0;
  transition: box-shadow 0.2s, opacity 0.2s;
}
.card:hover { box-shadow: 0 4px 18px rgba(0, 0, 0, 0.06); }
.card.done { opacity: 0.6; }
.card.flash { animation: flash 1.4s ease-out; }
@keyframes flash { 0% { box-shadow: 0 0 0 4px #ffd166; } 100% { box-shadow: none; } }

.card-head { display: flex; gap: 10px; align-items: flex-start; justify-content: space-between; }
.card-head h3 { margin: 0; font-size: 1.05rem; }
.card-head h3 .pid { color: var(--c); font-family: Consolas, monospace; margin-right: 6px; }

.meta { display: flex; flex-wrap: wrap; gap: 6px; margin: 6px 0 4px; }
.badge {
  font-size: 0.72rem;
  padding: 2px 8px;
  border-radius: 99px;
  background: #f0efea;
  color: #444;
  white-space: nowrap;
}
.badge.d1 { background: #e5f6ec; color: #13703f; }
.badge.d2 { background: #fff2dc; color: #8a5300; }
.badge.d3 { background: #fde4e4; color: #a01818; }
.badge.hw { background: #1d1d1f; color: #ffd166; }

.done-box { font-size: 0.8rem; color: var(--muted); display: flex; gap: 5px; align-items: center; white-space: nowrap; cursor: pointer; }

.statement { margin-top: 6px; }
.statement p:first-child { margin-top: 4px; }

details {
  margin: 8px 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fbfaf7;
}
details > summary {
  cursor: pointer;
  padding: 7px 12px;
  font-weight: 600;
  font-size: 0.88rem;
  list-style: none;
  user-select: none;
}
details > summary::-webkit-details-marker { display: none; }
details > summary::before { content: "▸ "; color: var(--muted); }
details[open] > summary::before { content: "▾ "; }
details.hint > summary { color: #8a5300; }
details.sol > summary { color: #13703f; }
details .body { padding: 2px 16px 10px; border-top: 1px dashed var(--line); }

code, .mono { font-family: Consolas, "Cascadia Code", monospace; font-size: 0.9em; background: #f1efe9; padding: 1px 5px; border-radius: 4px; }
pre { background: #1d1d1f; color: #f1f1f1; padding: 12px 14px; border-radius: 8px; overflow-x: auto; font-size: 0.85rem; line-height: 1.45; }
pre code { background: none; padding: 0; color: inherit; }

table.mini { border-collapse: collapse; margin: 8px 0; font-size: 0.88rem; }
table.mini td, table.mini th { border: 1px solid var(--line); padding: 4px 10px; text-align: center; }
table.mini th { background: #f1efe9; }

.empty { text-align: center; color: var(--muted); padding: 60px 0; }

.legend { font-size: 0.82rem; color: var(--muted); margin-top: 10px; }

footer { text-align: center; color: var(--muted); font-size: 0.8rem; padding: 30px; }
footer a { color: inherit; }

@media (max-width: 640px) {
  header.top h1 { font-size: 1.4rem; }
  .card { padding: 14px; }
}

@media print {
  .toolbar, .done-box { display: none; }
  details { border: none; }
  details:not([open]) .body { display: block; }
  .card { break-inside: avoid; }
}