:root {
  --cell-input-bg: #ffffff;
  --cell-input-fg: #1a1a1a;
  --cell-carry-bg: #fff7d6;
  --cell-carry-border: #facc15;
  --cell-blocked-bg: #f3f4f6;
  --cell-blocked-border: #e5e7eb;
  --cell-header-bg: #1f2937;
  --cell-header-fg: #ffffff;
  --cell-given-bg: #eff6ff;
  --cell-sum-bg: #ecfdf5;
  --border: #d1d5db;
  --border-strong: #374151;
  --ok: #16a34a;
  --bad: #dc2626;
  --hint: #9ca3af;
  --bg: #f8fafc;
  --panel: #ffffff;
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --secondary: #6b7280;
  --secondary-hover: #4b5563;
  --accent: #6d28d9;
  --celebrate: #facc15;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--cell-input-fg);
  -webkit-text-size-adjust: 100%;
}

body {
  padding-bottom: env(safe-area-inset-bottom);
}

.topbar {
  background: var(--panel);
  padding: 0.9rem 1.5rem;
  padding-top: max(0.9rem, env(safe-area-inset-top));
  padding-left: max(1.5rem, env(safe-area-inset-left));
  padding-right: max(1.5rem, env(safe-area-inset-right));
  border-bottom: 1px solid #e5e7eb;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.topbar-row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.topbar h1 {
  font-size: 1.4rem;
  margin: 0;
  letter-spacing: -0.02em;
  color: #111827;
}

.score {
  font-size: 0.95rem;
  background: #fef3c7;
  color: #78350f;
  padding: 0.3rem 0.75rem;
  border-radius: 999px;
  font-weight: 600;
  border: 1px solid #fde68a;
}

.score #score-count {
  font-weight: 700;
}

.problem-entry {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.entry-inputs {
  display: flex;
  align-items: center;
  gap: 0.55rem;
  flex-wrap: nowrap;
}

.entry-label {
  font-size: 1rem;
  font-weight: 600;
  color: #1f2937;
}

.num-input {
  font-size: 1.5rem;
  font-weight: 700;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  padding: 0.4rem 0.6rem;
  width: 110px;
  min-height: 48px;
  text-align: center;
  border: 2px solid #d1d5db;
  border-radius: 6px;
  background: white;
  color: #111827;
}

.num-input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.num-input::placeholder {
  color: #d1d5db;
  font-weight: 400;
}

.num-input.invalid {
  border-color: var(--bad);
  background: #fef2f2;
}

.times, .equals {
  font-size: 1.5rem;
  font-weight: 600;
  color: #374151;
  font-family: "SF Mono", Menlo, Consolas, monospace;
}

.equals {
  color: #6b7280;
}

.entry-help {
  font-size: 0.8rem;
  color: #6b7280;
}

.controls {
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.random-options {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.primary-actions,
.secondary-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: nowrap;
}

.primary-actions .primary,
.secondary-actions .secondary {
  flex: 1 1 0;
  white-space: nowrap;
}

.group-label {
  font-size: 0.85rem;
  color: #6b7280;
}

.times-sm {
  font-size: 1rem;
  color: #6b7280;
}

.controls select {
  font-size: 0.95rem;
  padding: 0.45rem 0.5rem;
  min-height: 40px;
  border: 1px solid #d4d4d4;
  border-radius: 4px;
  background: white;
}

.controls .checkbox {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.85rem;
  color: #4b5563;
  cursor: pointer;
}

.controls input[type="checkbox"] {
  width: 1rem;
  height: 1rem;
  margin: 0;
  cursor: pointer;
}

.controls button {
  font-size: 0.95rem;
  padding: 0.65rem 1.1rem;
  min-height: 44px;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  font-weight: 600;
  transition: background 0.15s ease, transform 0.05s ease;
  -webkit-tap-highlight-color: transparent;
}

.controls button:active { transform: translateY(1px); }

.controls button.primary {
  background: var(--primary);
  color: white;
}
.controls button.primary:hover { background: var(--primary-hover); }

.controls button.primary.big {
  font-size: 1.05rem;
  padding: 0.75rem 1.35rem;
  min-height: 48px;
}

.controls button.secondary {
  background: var(--secondary);
  color: white;
}
.controls button.secondary:hover { background: var(--secondary-hover); }

main {
  padding: 1.5rem 1rem 2rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}

.grid-scroll {
  max-width: 100%;
  overflow-x: auto;
  padding: 0.25rem;
}

.problem-label {
  font-size: 1.4rem;
  color: #111827;
  font-weight: 600;
  font-family: "SF Mono", Menlo, Consolas, monospace;
}

.grid {
  display: grid;
  background: white;
  border: 2px solid var(--border-strong);
  font-family: "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
  border-radius: 6px;
  width: max-content;
}

.cell {
  border: 1px solid var(--border);
  width: 72px;
  height: 72px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.6rem;
  font-weight: 500;
  position: relative;
  background: var(--cell-input-bg);
}

.cell.header {
  background: var(--cell-header-bg);
  color: var(--cell-header-fg);
  font-weight: 700;
  font-size: 0.78rem;
  letter-spacing: -0.01em;
  overflow: hidden;
}
.cell.header[data-len="7"] { font-size: 0.72rem; }
.cell.header[data-len="8"] { font-size: 0.68rem; }
.cell.header[data-len="9"] { font-size: 0.62rem; }
.cell.header[data-len="10"] { font-size: 0.56rem; }

.cell.margin {
  border: none;
  font-size: 1.5rem;
  font-weight: 500;
  background: transparent;
  width: 40px;
  height: 72px;
  padding-right: 6px;
  justify-content: flex-end;
  color: #1f2937;
  font-family: -apple-system, BlinkMacSystemFont, sans-serif;
}

.cell.black {
  background: var(--cell-blocked-bg);
}

.cell.carry {
  background: var(--cell-carry-bg);
  font-size: 0.95rem;
}

.cell.given {
  background: var(--cell-given-bg);
  font-weight: 700;
}

.cell.given.active-step {
  background: #fde68a;
  box-shadow: inset 0 0 0 3px #f59e0b;
  animation: pulse-step 1.5s ease-in-out infinite;
}

@keyframes pulse-step {
  0%, 100% { box-shadow: inset 0 0 0 3px #f59e0b; }
  50% { box-shadow: inset 0 0 0 3px #fbbf24; }
}

.cell.sum-cell {
  background: var(--cell-sum-bg);
}

.cell.mistake {
  background: #fee2e2;
}

.cell input {
  width: 100%;
  height: 100%;
  border: none;
  outline: none;
  background: transparent;
  text-align: center;
  font-size: inherit;
  font-weight: inherit;
  font-family: inherit;
  color: inherit;
  padding: 0;
  -moz-appearance: textfield;
}
.cell input::-webkit-outer-spin-button,
.cell input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

.cell input:focus {
  outline: 3px solid var(--primary);
  outline-offset: -3px;
  background: transparent;
}

.cell.carry input {
  font-size: 1.05rem;
  color: var(--accent);
  font-weight: 700;
}

.cell.divider-bottom {
  border-bottom: 2px solid var(--border-strong);
}

.cell.wrong {
  background: #fee2e2;
}
.cell.correct input {
  color: var(--ok);
}
.cell.wrong input {
  color: var(--bad);
}
.cell.carry.wrong input,
.cell.carry.mistake input {
  color: #374151;
}
.cell.revealed input {
  color: var(--hint);
  font-style: italic;
}

.cell.celebrate {
  animation: celebrate 0.6s ease;
}

@keyframes celebrate {
  0%, 100% { background: var(--cell-input-bg); }
  50% { background: var(--celebrate); }
}

.status {
  font-size: 1.05rem;
  min-height: 1.5rem;
  font-weight: 600;
  padding: 0.5rem 1rem;
  border-radius: 6px;
}
.status.ok {
  background: #dcfce7;
  color: var(--ok);
}
.status.bad {
  background: #fee2e2;
  color: var(--bad);
}

.help {
  font-size: 0.9rem;
  color: #4b5563;
  background: white;
  border: 1px solid #e5e7eb;
  border-radius: 6px;
  padding: 0.5rem 0.85rem;
  max-width: 540px;
}

.help summary {
  cursor: pointer;
  font-weight: 600;
  color: #111827;
}

.help-body p {
  margin: 0.5rem 0;
  line-height: 1.45;
}

.help kbd {
  font-family: "SF Mono", Menlo, Consolas, monospace;
  background: #f3f4f6;
  padding: 0.1rem 0.35rem;
  border-radius: 3px;
  border: 1px solid #e5e7eb;
  font-size: 0.85rem;
}

.link-button {
  background: none;
  border: none;
  color: var(--primary);
  text-decoration: underline;
  cursor: pointer;
  font-size: 0.85rem;
  padding: 0;
  font-family: inherit;
}
.link-button:hover { color: var(--primary-hover); }

.swatch {
  display: inline-block;
  width: 14px;
  height: 14px;
  border-radius: 3px;
  vertical-align: -2px;
  margin-right: 2px;
  border: 1px solid var(--border);
}
.swatch-given { background: var(--cell-given-bg); }
.swatch-carry { background: var(--cell-carry-bg); border-color: var(--cell-carry-border); }
.swatch-input { background: var(--cell-input-bg); }
.swatch-sum { background: var(--cell-sum-bg); }
.swatch-blocked { background: var(--cell-blocked-bg); border-color: var(--cell-blocked-border); }

.help code {
  background: #f3f4f6;
  padding: 0.1rem 0.3rem;
  border-radius: 3px;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.85em;
}

@media print {
  .topbar, .status, .help { display: none; }
  body { background: white; }
  main { padding-top: 0.5rem; }
  .grid { border-color: #000; }
  .cell { border-color: #6b7280; }
  .cell.header { background: #1f2937 !important; color: #fff !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .cell.given { background: #eff6ff !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .cell.carry { background: #fef3c7 !important; border-color: #d97706 !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .cell.sum-cell { background: #ecfdf5 !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .cell.black { background: #e5e7eb !important; border-color: #d1d5db !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .cell input:focus { background: transparent; }
}