:root {
  --bg: #f6f3ee;
  --ink: #1c1917;
  --muted: #78716c;
  --line: #e7e5e4;
  --card: #fffdf9;
  --accent: #0f766e;
  --accent-ink: #ecfdf5;
  --warn-bg: #fff7ed;
  --flow-bg: #f5f3ff;
  --config-bg: #eff6ff;
  --explain-bg: #f0fdf4;
  --font: "IBM Plex Sans", "Source Han Sans SC", "Noto Sans SC", system-ui, sans-serif;
  --mono: "IBM Plex Mono", ui-monospace, monospace;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: var(--font);
  color: var(--ink);
  background:
    radial-gradient(1200px 500px at 10% -10%, #dbeafe 0%, transparent 55%),
    radial-gradient(900px 400px at 100% 0%, #ccfbf1 0%, transparent 50%),
    var(--bg);
  min-height: 100vh;
}

.top {
  padding: 1.25rem 1.5rem 0.75rem;
  border-bottom: 1px solid var(--line);
  background: rgba(255, 253, 249, 0.85);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
  z-index: 10;
}
.brand {
  font-size: 1.75rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}
.tag { margin: 0.2rem 0 0.9rem; color: var(--muted); font-size: 0.95rem; }
.tabs { display: flex; gap: 0.4rem; flex-wrap: wrap; }
.tabs button {
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  border-radius: 999px;
  padding: 0.4rem 0.95rem;
  cursor: pointer;
  font: inherit;
}
.tabs button.active {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-ink);
}

main { padding: 1.25rem 1.5rem 2.5rem; max-width: 1100px; margin: 0 auto; }
.panel { display: none; }
.panel.active { display: block; }

.row { display: flex; gap: 0.6rem; align-items: end; margin-bottom: 0.75rem; }
.row.wrap { flex-wrap: wrap; }
.grow { flex: 1 1 12rem; }
.block { display: block; width: 100%; margin-bottom: 0.75rem; }
label {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  font-size: 0.8rem;
  color: var(--muted);
}
label.check { flex-direction: row; align-items: center; gap: 0.4rem; padding-bottom: 0.35rem; }
input, select, textarea, button {
  font: inherit;
  color: var(--ink);
}
input, select, textarea {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0.45rem 0.55rem;
  background: #fff;
}
textarea { width: 100%; font-family: var(--mono); font-size: 0.82rem; resize: vertical; }
button {
  border: 1px solid var(--line);
  background: #fff;
  border-radius: 8px;
  padding: 0.5rem 0.85rem;
  cursor: pointer;
}
button.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-ink);
}
button:disabled { opacity: 0.55; cursor: not-allowed; }

.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 0.9rem 1rem;
  margin-bottom: 0.75rem;
}
.pr-config { background: var(--config-bg); }
.pr-controls { background: var(--warn-bg); }
.pr-flow { background: var(--flow-bg); }
.pr-explain { background: var(--explain-bg); }
.pr-vars { background: #eff6ff; }
.label { font-size: 0.8rem; color: var(--muted); margin-bottom: 0.4rem; }
.muted { color: var(--muted); }
.split {
  display: grid;
  grid-template-columns: 1fr 1.4fr;
  gap: 0.75rem;
}
@media (max-width: 800px) {
  .split { grid-template-columns: 1fr; }
}

.flow { display: flex; flex-wrap: wrap; gap: 0.4rem; }
.flow button {
  font-size: 0.8rem;
  padding: 0.35rem 0.55rem;
}
.flow button.current {
  background: #4c1d95;
  border-color: #4c1d95;
  color: #fff;
}

.md { font-size: 0.92rem; line-height: 1.55; }
.md pre, .md code { font-family: var(--mono); font-size: 0.84rem; }
.md img { max-width: 100%; }
.md .katex { font-size: 1.05em; }
.md .katex-display { margin: 0.75rem 0; overflow-x: auto; overflow-y: hidden; }
.md .math-error { color: #b91c1c; white-space: pre-wrap; }
#pr-value-img { max-width: 100%; border-radius: 8px; margin-top: 0.5rem; border: 1px solid var(--line); }

.chat {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #fff;
  min-height: 280px;
  max-height: 420px;
  overflow: auto;
  padding: 0.75rem;
  margin-bottom: 0.75rem;
}
.bubble { margin-bottom: 0.65rem; padding: 0.55rem 0.7rem; border-radius: 10px; }
.bubble.user { background: #ecfeff; }
.bubble.assistant { background: #f5f5f4; }
.bubble .role { font-size: 0.72rem; color: var(--muted); margin-bottom: 0.2rem; }