:root {
  --bg: #ffffff;
  --fg: #111111;
  --muted: #666666;
  --surface: #f4f4f5;
  --primary: #2563eb;
  --primary-contrast: #ffffff;
  --correct: #22c55e;
  --wrong: #ef4444;
  --warning: #f59e0b;
  color-scheme: light dark;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b0b0c;
    --fg: #f3f4f6;
    --muted: #a1a1aa;
    --surface: #17171a;
    --primary: #60a5fa;
    --primary-contrast: #0b0b0c;
    --correct: #22c55e;
    --wrong: #f87171;
    --warning: #fbbf24;
  }
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: 'Inter', system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, 'Apple Color Emoji', 'Segoe UI Emoji';
  background: var(--bg);
  color: var(--fg);
  display: grid;
  grid-template-rows: auto 1fr auto;
  grid-template-columns: minmax(0, 1fr);
}

.app-header, .app-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 20px;
}
.app-header h1 { font-weight: 800; font-size: 20px; margin: 0; }
.status { color: var(--muted); font-size: 14px; }

.app-main { max-width: 720px; width: 100%; margin: 0 auto; padding: 12px 20px 24px; }

.gen-form { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr) auto auto; gap: 10px; margin-bottom: 12px; align-items: center; }
.gen-form input { min-width: 0; background: var(--surface); color: var(--fg); border: 1px solid transparent; border-radius: 10px; padding: 10px 12px; }
.gen-form button { white-space: nowrap; }
.gen-form input[readonly] { color: var(--muted); }
.demo-note { margin: -4px 0 14px; color: var(--muted); font-size: 14px; line-height: 1.5; }
.demo-note a, .app-footer a.link { color: var(--primary); }
.app-footer a.link { font-size: 14px; }

.solved { display: grid; grid-template-columns: 1fr; gap: 8px; margin-bottom: 12px; }
.solved .group {
  background: var(--surface);
  border-radius: 10px;
  padding: 10px 12px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-weight: 600;
  border: 2px solid transparent;
}

.grid { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 10px; }
.tile {
  user-select: none;
  background: var(--surface);
  border-radius: 12px;
  padding: 18px 10px;
  text-align: center;
  font-weight: 600;
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 2px solid transparent;
  transition: transform 120ms ease, box-shadow 120ms ease, background 120ms ease, border-color 120ms ease;
  container-type: inline-size;
}
/* Uppercase bold letters average about 0.68em wide, so this keeps the longest word on one line */
.tile span { font-size: min(1em, calc(100cqw / (var(--len, 8) * 0.68))); overflow-wrap: break-word; }
.tile:hover { transform: translateY(-1px); }
.tile.selected { outline: none; border-color: var(--primary); box-shadow: 0 0 0 3px color-mix(in oklab, var(--primary) 30%, transparent); }
.tile.locked { background: color-mix(in oklab, var(--correct) 18%, var(--surface)); border-color: var(--correct); }
.tile.wrong { background: color-mix(in oklab, var(--wrong) 18%, var(--surface)); }

.controls { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; margin: 16px 0 10px; }
.controls .spacer { flex: 1; }

button { font: inherit; border-radius: 10px; padding: 10px 14px; border: 1px solid transparent; cursor: pointer; }
button.primary { background: var(--primary); color: var(--primary-contrast); }
button.secondary { background: var(--surface); color: var(--fg); }
button.link { background: transparent; color: var(--muted); text-decoration: underline; border-color: transparent; }
button:disabled { opacity: 0.5; cursor: not-allowed; }
button.primary:disabled { background: var(--surface); color: var(--muted); }

.message { min-height: 24px; color: var(--muted); }
.message.success { color: var(--correct); }
.message.error { color: var(--wrong); }
.message.warn { color: var(--warning); }

.explanation { margin-top: 8px; color: var(--muted); white-space: pre-wrap; line-height: 1.5; }
.notes { margin-top: 8px; color: var(--muted); white-space: pre-wrap; line-height: 1.6; }
.notes > div { margin: 8px 0 12px; }
.answers { margin-top: 8px; background: var(--surface); border-radius: 10px; padding: 12px; }
.answers .answer { padding: 8px 6px; border-bottom: 1px dashed color-mix(in oklab, var(--muted) 35%, transparent); }
.answers .answer:last-child { border-bottom: none; }
.answers .label { font-weight: 700; }
.recommendations { margin-top: 8px; }
.recommendations > div { margin: 6px 0; }
.recommendations a { color: var(--primary); text-decoration: none; }
.recommendations a:hover { text-decoration: underline; }

/* Celebrations */
.confetti { position: fixed; top: -10px; width: 10px; height: 14px; opacity: 0.9; border-radius: 2px; pointer-events: none; animation: fall linear forwards; }
@keyframes fall { to { transform: translateY(110vh) rotate(720deg); opacity: 0.95; } }

.spark { position: fixed; width: 6px; height: 6px; border-radius: 50%; pointer-events: none; transform: translate(-50%, -50%); animation: burst 2.2s ease-out forwards; }
@keyframes burst { to { transform: translate(calc(-50% + var(--tx)), calc(-50% + var(--ty))); opacity: 0; } }

@media (max-width: 520px) {
  .tile { padding: 14px 5px; min-height: 56px; font-size: 13px; }
  .grid { gap: 6px; }
  .app-main { padding: 8px 16px 20px; }
  .app-header, .app-footer { padding: 14px 16px; }
  .gen-form { grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); }
  .controls button { padding: 10px 12px; }
  .gen-form button { grid-column: 1 / -1; }
  .solved .group { flex-direction: column; align-items: flex-start; gap: 2px; }
}

/* Loader badge (bottom-right mini) */
.loader { position: relative; z-index: 10; display: flex; align-items: center; gap: 0; padding: 0; margin-left: 6px; background: transparent; border: 0; box-shadow: none; }
.loader[hidden] { display: none !important; }
.loader-text { display: none; }
@keyframes pulse { 0%,100%{opacity:.6} 50%{opacity:1} }

/* Tiny robot reading a paper */
.robot { position: relative; width: 28px; height: 28px; animation: bounce 1.2s ease-in-out infinite; }
@keyframes bounce { 0%,100%{ transform: translateY(0); } 50% { transform: translateY(-4px); } }
.robot .head { position: absolute; top: 0; left: 50%; transform: translateX(-50%); width: 14px; height: 10px; background: #9ca3af; border-radius: 4px; box-shadow: inset 0 -1px 0 #6b7280; }
.robot .head::before, .robot .head::after { content:''; position: absolute; top: 3px; width: 3px; height: 3px; background: #111; border-radius: 50%; animation: blink 4s infinite; }
.robot .head::before { left: 3px; }
.robot .head::after { right: 3px; }
@keyframes blink { 0%,48%,52%,100%{ transform: scaleY(1);} 50%{ transform: scaleY(0.1);} }
.robot .body { position:absolute; top:8px; left:50%; transform: translateX(-50%); width: 18px; height: 12px; background:#d1d5db; border-radius: 3px; box-shadow: inset 0 -1px 0 #9ca3af; }
.robot .paper { position:absolute; top:7px; left:50%; transform: translateX(-50%) rotateX(8deg); width: 20px; height: 13px; background:#fff; border:1px solid #e5e7eb; border-radius:3px; box-shadow: 0 2px 6px rgba(0,0,0,.06); animation: rustle 1.8s ease-in-out infinite; }
@keyframes rustle { 0%,100% { transform: translateX(-50%) rotateX(8deg) rotateZ(-2deg); } 50% { transform: translateX(-50%) rotateX(10deg) rotateZ(2deg); } }