:root {
  --bg: #e8edf4;
  --card: #ffffff;
  --ink: #182742;
  --muted: #64748b;
  --line: #d8e0ec;
  --accent: #1d4ed8;
  --accent-ink: #173da0;
  --accent-soft: #e2ebfd;
  --related: #f1f6fe;
  --same: #d5e4fc;
  --error: #dc2626;
  --error-bg: #fee2e2;
  --good: #047857;
  --good-bg: #e2f4eb;
  --radius: 12px;
  --shadow: 0 1px 2px rgba(24, 39, 66, 0.06), 0 10px 28px rgba(24, 39, 66, 0.10);
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--ink);
  min-height: 100vh;
  display: flex;
  justify-content: center;
}
.app { width: 100%; max-width: 560px; padding: 20px 16px 28px; display: flex;
  flex-direction: column; align-items: center; gap: 14px; }
#screen-start, #screen-game { display: flex; flex-direction: column;
  align-items: center; gap: 13px; width: 100%; }
h1 { margin: 6px 0 0; font-size: 1.9rem; letter-spacing: -0.01em; text-align: center; }
#level-name {
  display: inline-block; vertical-align: middle;
  font-size: 0.8rem; font-weight: 700; letter-spacing: 0.02em;
  color: var(--accent-ink); background: var(--accent-soft);
  border-radius: 999px; padding: 3px 12px; margin-left: 6px;
}
.hidden { display: none !important; }
button {
  font: inherit; font-size: 1rem; padding: 10px 14px; border-radius: var(--radius);
  border: 1px solid var(--line); background: var(--card); color: var(--ink);
  cursor: pointer; touch-action: manipulation;
  transition: border-color 0.12s ease, background 0.12s ease, transform 0.05s ease;
}
button:hover { border-color: var(--accent); background: #fbfdff; }
button:active { transform: scale(0.97); }
button:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
button.primary { background: var(--accent); border-color: var(--accent); color: #fff;
  font-weight: 700; box-shadow: 0 4px 12px rgba(29, 78, 216, 0.28); }
button.primary:hover { background: #1a45bd; }
button.on { background: var(--accent-soft); border-color: var(--accent);
  color: var(--accent-ink); font-weight: 600; }
button:disabled { opacity: 0.55; cursor: default; }
.levels { display: grid; grid-template-columns: repeat(2, 1fr); gap: 10px; width: min(92vw, 440px); }
.levels button { padding: 16px 6px; font-weight: 700; font-size: 1.05rem;
  box-shadow: 0 1px 2px rgba(24, 39, 66, 0.06); }
.levels button:hover { background: var(--accent-soft); }
.levels small { display: block; font-weight: 400; font-size: 0.75rem; color: var(--muted); margin-top: 2px; }
.seedrow { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; justify-content: center; }
.seedrow input { width: 6em; padding: 9px 10px; font: inherit; font-size: 1rem;
  border-radius: var(--radius); border: 1px solid var(--line); background: var(--card); }
.help { font-size: 0.85rem; color: var(--muted); max-width: 460px; text-align: center; margin: 0; }
.help kbd { background: #fff; border: 1px solid var(--line); border-bottom-width: 2px;
  border-radius: 6px; padding: 0 6px; font-size: 0.78rem; font-family: inherit; }
.toolbar { display: flex; gap: 8px; align-items: center; flex-wrap: wrap; justify-content: center; }
.stats { display: grid; grid-template-columns: repeat(4, 1fr); gap: 8px;
  width: min(92vw, 440px); font-variant-numeric: tabular-nums; }
.stats > span {
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 7px 4px 8px; text-align: center;
  font-size: 0.66rem; font-weight: 700; letter-spacing: 0.07em;
  text-transform: uppercase; color: var(--muted);
}
.stats > span > span {
  display: block; font-size: 1.12rem; font-weight: 700; color: var(--ink);
  letter-spacing: 0; text-transform: none; margin-top: 1px;
}
.board { display: grid; grid-template-columns: repeat(9, 1fr);
  width: min(92vw, 440px); aspect-ratio: 1;
  border: 2px solid var(--ink); border-radius: var(--radius); overflow: hidden;
  background: var(--ink); box-shadow: var(--shadow); }
.cell { display: flex; align-items: center; justify-content: center;
  font-size: clamp(1.15rem, 5vw, 1.65rem); font-weight: 500; color: var(--accent-ink);
  background: #fff; cursor: pointer; user-select: none; position: relative;
  border-right: 1px solid var(--line); border-bottom: 1px solid var(--line);
  transition: background 0.12s ease; }
.cell:nth-child(9n + 3), .cell:nth-child(9n + 6) { border-right: 2px solid var(--ink); }
.cell:nth-child(n + 19):nth-child(-n + 27),
.cell:nth-child(n + 46):nth-child(-n + 54) { border-bottom: 2px solid var(--ink); }
.cell.given { background: #f6f9fd; color: var(--ink); font-weight: 700; cursor: default; }
.cell.hinted { color: var(--good); background: var(--good-bg); font-weight: 700; cursor: default; }
.cell.selected { background: var(--accent-soft); outline: 2px solid var(--accent); outline-offset: -2px; }
.cell.related { background: var(--related); }
.cell.same { background: var(--same); font-weight: 700; }
.cell.conflict { color: var(--error); background: var(--error-bg); }
.cell .notes { display: grid; grid-template-columns: repeat(3, 1fr);
  width: 100%; height: 100%; font-size: clamp(0.5rem, 2vw, 0.65rem);
  color: #475569; font-weight: 400; }
.cell .notes span { display: flex; align-items: center; justify-content: center; }
.pad { display: grid; grid-template-columns: repeat(5, 1fr); gap: 8px; width: min(92vw, 440px); }
.pad button { font-size: 1.3rem; font-weight: 700; padding: 12px 0; color: var(--ink);
  box-shadow: 0 1px 2px rgba(24, 39, 66, 0.06); }
.pad button:last-child { font-size: 0.9rem; }
.pad button.active { background: var(--accent); border-color: var(--accent); color: #fff; }
.actions { display: grid; grid-template-columns: repeat(3, 1fr); gap: 8px; width: min(92vw, 440px); }
.actions button { padding: 10px 4px; font-size: 0.88rem; font-weight: 600; }
#btn-new2 { border-color: var(--accent); color: var(--accent-ink); }
.message { min-height: 1.6em; margin: 0; text-align: center; font-weight: 600; font-size: 0.95rem; }
.message.success { color: var(--good); }
.message.warning { color: #b45309; }
.message.error { color: var(--error); }
.veil { position: fixed; inset: 0; background: rgba(15, 23, 42, 0.92); color: #fff;
  display: flex; flex-direction: column; gap: 12px; align-items: center; justify-content: center;
  z-index: 30; text-align: center; padding: 16px; }
.panel { background: var(--card); color: var(--ink); border-radius: 16px; padding: 24px;
  max-width: min(92vw, 440px); display: flex; flex-direction: column; gap: 12px;
  align-items: center; text-align: center; box-shadow: var(--shadow); }
.panel h2 { margin: 0 0 4px; letter-spacing: -0.01em; }
.panel p { margin: 0; }
.debug { position: fixed; left: 8px; bottom: 8px; z-index: 40; background: #0f172a; color: #e2e8f0;
  font-family: monospace; font-size: 0.75rem; border-radius: 8px; padding: 10px 12px;
  max-width: min(94vw, 460px); max-height: 60vh; overflow: auto; }
.debug table { border-collapse: collapse; }
.debug td { padding: 1px 8px 1px 0; }
.debug input { width: 5em; font: inherit; }
.debug button { font-size: 0.75rem; padding: 4px 8px; }
#autotest-results { white-space: pre-wrap; }
.pass { color: #4ade80; } .fail { color: #f87171; }
@media (min-width: 920px) {
  .app { max-width: 940px; }
  #screen-game { display: grid; grid-template-columns: minmax(0, 440px) 320px;
    gap: 14px 20px; justify-content: center; align-items: start; }
  #screen-game h1 { grid-column: 1 / -1; }
  #screen-game .board { grid-column: 1; grid-row: 2 / span 3; width: 100%; max-width: 460px; }
  #screen-game .stats { grid-column: 2; grid-row: 2; width: 100%; grid-template-columns: repeat(2, 1fr); }
  #screen-game .pad { grid-column: 2; grid-row: 3; width: 100%; }
  #screen-game .actions { grid-column: 2; grid-row: 4; width: 100%; }
  #screen-game .message { grid-column: 1 / -1; }
  #screen-game .help { grid-column: 1 / -1; }
}
@media (max-width: 420px) {
  .app { padding: 14px 10px 24px; }
  .stats { grid-template-columns: repeat(2, 1fr); }
  h1 { font-size: 1.6rem; }
}