*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI',
    'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', sans-serif;
  background: #f5f7fb;
  color: #1f2933;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.container {
  width: 100%;
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 16px;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: #ffffff;
  border-bottom: 1px solid #e5e7eb;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 56px;
}

.brand-title {
  font-size: 18px;
  font-weight: 600;
  letter-spacing: 0.02em;
  color: #111827;
}

.brand-subtitle {
  display: inline-block;
  margin-left: 10px;
  font-size: 12px;
  color: #9ca3af;
}

.main {
  flex: 1;
  padding-top: 16px;
  padding-bottom: 24px;
}

.app-layout {
  display: grid;
  grid-template-columns: 220px minmax(0, 1fr);
  gap: 16px;
}

.sidebar {
  align-self: flex-start;
  background: #ffffff;
  border-radius: 6px;
  padding: 10px 0;
  border: 1px solid #e5e7eb;
  box-shadow: 0 1px 3px rgba(15, 23, 42, 0.06);
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.sidebar-section {
  padding: 4px 0 8px;
  border-bottom: 1px solid #f1f2f6;
  padding-inline: 8px;
}

.sidebar-section:last-child {
  border-bottom: none;
}

.sidebar-title {
  font-size: 12px;
  color: #9ca3af;
  margin: 4px 4px 6px;
}

.app-content {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.nav-tab {
  width: 100%;
  border-radius: 4px;
  border: 1px solid transparent;
  background: transparent;
  color: #374151;
  font-size: 14px;
  padding: 6px 10px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: flex-start;
  gap: 8px;
  transition: background 0.12s ease, border-color 0.12s ease, color 0.12s ease;
}

.nav-tab::before {
  content: '';
  width: 16px;
  height: 16px;
  border-radius: 4px;
  background: #e5e7eb;
  display: inline-block;
}

.nav-tab.active::before {
  background: #3b82f6;
}

.nav-tab:hover {
  background: #f3f4f6;
}

.nav-tab.active {
  background: #e5f0ff;
  border-color: #3b82f6;
  color: #1d4ed8;
}

.panel {
  background: #ffffff;
  border-radius: 6px;
  padding: 18px 18px 16px;
  box-shadow: 0 1px 3px rgba(15, 23, 42, 0.08);
  border: 1px solid #e5e7eb;
}

.panel-secondary {
  margin-top: 4px;
  background: #ffffff;
}

.panel-title {
  margin: 0 0 6px;
  font-size: 22px;
}

.panel-desc {
  margin: 0 0 16px;
  font-size: 13px;
  color: #6b7280;
}

.game-panel {
  margin-bottom: 18px;
}

.game-panel[hidden] {
  display: none;
}

.subtab-btn {
  width: 100%;
  border: none;
  background: transparent;
  color: #6b7280;
  font-size: 13px;
  padding: 4px 10px;
  border-radius: 8px;
  cursor: pointer;
  text-align: left;
  transition: background 0.16s ease, color 0.16s ease, transform 0.08s ease;
}

.subtab-btn.active {
  background: #eff6ff;
  color: #1d4ed8;
}

.subtab-btn:hover {
  background: #f3f4f6;
}

.subpage {
  margin-top: 4px;
}

.subpage[hidden] {
  display: none;
}

.play-toolbar {
  margin-top: 14px;
  margin-bottom: 0;
  width: 100%;
  display: flex;
  justify-content: center;
}

.toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 18px;
}

.play-controls {
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: 10px;
  font-size: 13px;
}

.play-controls-compact {
  max-width: calc(var(--cell-size) * 9 + 6px * 2 + 2px * 2);
}

.solve-toolbar {
  margin-top: 12px;
  margin-bottom: 0;
  width: 100%;
  display: flex;
  justify-content: center;
}

.solve-controls {
  width: 100%;
  max-width: calc(var(--cell-size) * 9 + 6px * 2 + 2px * 2);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
}

.play-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
}

.timer-label {
  min-width: 90px;
  text-align: center;
  color: #4b5563;
}

.level-select-wrapper {
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.level-select {
  border-radius: 4px;
  border: 1px solid #d1d5db;
  padding: 4px 6px;
  font-size: 13px;
  background: #ffffff;
  color: #374151;
}

.level-select:focus {
  outline: none;
  border-color: #2563eb;
  box-shadow: 0 0 0 1px rgba(37, 99, 235, 0.2);
}

.play-btn {
  min-width: 60px;
  padding-inline: 10px;
}

.size-selector {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  font-size: 14px;
}

.size-selector .label {
  color: #9ca3af;
}

.size-btn {
  padding: 4px 10px;
  border-radius: 4px;
  border: 1px solid #d1d5db;
  background: #ffffff;
  color: #374151;
  font-size: 13px;
  cursor: pointer;
  transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease,
    transform 0.1s ease;
}

.size-btn.active {
  background: #2563eb;
  border-color: #2563eb;
  color: #ffffff;
  box-shadow: none;
}

.size-btn.disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.size-btn:not(.disabled):hover {
  transform: translateY(-1px);
  border-color: #e5e7eb;
}

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.btn {
  border-radius: 4px;
  border: 1px solid transparent;
  font-size: 14px;
  padding: 6px 14px;
  cursor: pointer;
  font-weight: 500;
  transition: background 0.16s ease, transform 0.1s ease,
    box-shadow 0.16s ease, border-color 0.16s ease, color 0.16s ease;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
}

.btn.primary {
  background: #2563eb;
  color: #ffffff;
}

.btn.primary:hover {
  background: #1d4ed8;
}

.btn.secondary {
  background: #ffffff;
  border-color: #d1d5db;
  color: #374151;
}

.btn.secondary:hover {
  background: #f3f4f6;
}

.btn.ghost {
  background: transparent;
  border-color: #d1d5db;
  color: #6b7280;
}

.btn.ghost:hover {
  border-color: #9ca3af;
  background: #f9fafb;
}

.btn.small {
  font-size: 13px;
  padding: 4px 10px;
}

.layout {
  display: grid;
  grid-template-columns: minmax(0, 3fr) minmax(0, 2fr);
  gap: 18px;
}

.grid-wrapper {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 10px;
}

.sudoku-grid {
  --cell-size: 40px;
  display: grid;
  grid-template-columns: repeat(9, var(--cell-size));
  grid-template-rows: repeat(9, var(--cell-size));
  background: #ffffff;
  border-radius: 6px;
  padding: 6px;
  border: 2px solid #4b5563;
  box-shadow: 0 1px 3px rgba(15, 23, 42, 0.08);
  position: relative;
}

.sudoku-cell {
  position: relative;
  border: 1px solid #e5e7eb;
  background: #ffffff;
}

.sudoku-input {
  width: 100%;
  height: 100%;
  border: none;
  outline: none;
  background: transparent;
  color: #2563eb;
  text-align: center;
  font-size: 18px;
  font-weight: 500;
  caret-color: #38bdf8;
}

.sudoku-input::placeholder {
  color: #d1d5db;
}

.sudoku-input[readonly] {
  color: #f97316;
}

.sudoku-cell.highlight {
  background: #e0f2fe;
}

.sudoku-cell.error {
  background: #fee2e2;
}

.sudoku-cell.prefilled .sudoku-input {
  color: #111827;
  font-weight: 600;
}

.sudoku-cell-border-right {
  border-right-width: 2px;
  border-right-color: #4b5563;
}

.sudoku-cell-border-bottom {
  border-bottom-width: 2px;
  border-bottom-color: #4b5563;
}

.hint {
  font-size: 12px;
  color: #9ca3af;
}

.side-panel {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.side-block {
  background: #f9fafb;
  border-radius: 6px;
  padding: 10px 10px 8px;
  border: 1px solid #e5e7eb;
}

.side-block h2 {
  margin: 0 0 6px;
  font-size: 15px;
}

.side-text {
  margin: 0 0 6px;
  font-size: 13px;
  color: #6b7280;
}

.example-inline {
  margin: 0 0 8px;
  padding: 6px 8px;
  border-radius: 4px;
  background: #111827;
  border: 1px solid #111827;
  font-size: 11px;
  color: #f9fafb;
  overflow-x: auto;
}

.bulk-input {
  width: 100%;
  border-radius: 4px;
  border: 1px solid #d1d5db;
  background: #ffffff;
  color: #111827;
  padding: 8px 9px;
  resize: vertical;
  font-size: 13px;
  outline: none;
}

.bulk-input:focus {
  border-color: #2563eb;
  box-shadow: 0 0 0 1px rgba(37, 99, 235, 0.3);
}

.side-actions {
  margin-top: 6px;
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.status-bar {
  font-size: 13px;
  padding: 7px 9px;
  border-radius: 9px;
  background: #ecfdf5;
  border: 1px solid #a7f3d0;
  color: #047857;
}

.status-bar.error {
  background: #fef2f2;
  border-color: #fecaca;
  color: #b91c1c;
}

.status-bar.warning {
  background: #fffbeb;
  border-color: #fef3c7;
  color: #92400e;
}

.site-footer {
  border-top: 1px solid #e5e7eb;
  padding: 10px 0 16px;
  background: #ffffff;
  font-size: 12px;
  color: #9ca3af;
}

@media (max-width: 900px) {
  .container {
    padding: 0 12px;
  }

  .header-inner {
    justify-content: center;
    height: 52px;
  }

  .brand-title {
    font-size: 16px;
  }

  .brand-subtitle {
    font-size: 11px;
  }

  .main {
    padding-top: 12px;
    padding-bottom: 16px;
  }

  .app-layout {
    grid-template-columns: minmax(0, 1fr);
    gap: 12px;
  }

  .sidebar {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    padding: 8px 0;
    gap: 0;
  }

  .sidebar-section {
    border-bottom: none;
    padding-bottom: 0;
    padding-inline: 6px;
    width: 50%;
  }

  .sidebar-title {
    margin-bottom: 4px;
    font-size: 11px;
  }

  .nav-tab,
  .subtab-btn {
    font-size: 12px;
    padding: 5px 8px;
  }

  .nav-tab::before {
    width: 12px;
    height: 12px;
  }

  .panel {
    padding: 14px 12px 12px;
  }

  .panel-title {
    font-size: 18px;
    margin-bottom: 4px;
  }

  .panel-desc {
    font-size: 12px;
    margin-bottom: 12px;
  }

  .layout {
    grid-template-columns: minmax(0, 1fr);
    gap: 12px;
  }

  .grid-wrapper {
    order: 1;
  }

  .side-panel {
    order: 2;
  }

  .sudoku-grid {
    --cell-size: min(38px, calc((100vw - 60px) / 9));
    padding: 6px;
  }

  .sudoku-input {
    font-size: 16px;
  }

  .toolbar {
    gap: 8px;
    margin-bottom: 12px;
  }

  .play-toolbar {
    gap: 6px;
    padding: 8px 0;
  }

  .play-toolbar-row {
    gap: 6px;
  }

  .btn {
    font-size: 13px;
    padding: 5px 10px;
  }

  .level-select {
    font-size: 12px;
    padding: 5px 8px;
  }

  .play-timer {
    font-size: 13px;
  }
}

@media (max-width: 600px) {
  .container {
    padding: 0 8px;
  }

  .header-inner {
    height: 48px;
  }

  .brand-title {
    font-size: 15px;
  }

  .main {
    padding-top: 8px;
    padding-bottom: 12px;
  }

  .sidebar {
    flex-direction: column;
    padding: 6px 0;
  }

  .sidebar-section {
    width: 100%;
    padding-inline: 8px;
    padding-bottom: 4px;
    border-bottom: 1px solid #f1f2f6;
  }

  .sidebar-section:last-child {
    border-bottom: none;
  }

  .nav-tab,
  .subtab-btn {
    font-size: 13px;
    padding: 6px 10px;
  }

  .panel {
    padding: 12px 10px 10px;
  }

  .panel-title {
    font-size: 17px;
  }

  .panel-desc {
    font-size: 11px;
  }

  .toolbar {
    flex-direction: column;
    align-items: stretch;
    gap: 8px;
  }

  .play-toolbar {
    padding: 6px 0;
  }

  .play-toolbar-row {
    flex-wrap: wrap;
    gap: 6px;
  }

  .size-selector {
    width: 100%;
    justify-content: flex-start;
  }

  .actions {
    width: 100%;
    justify-content: flex-start;
  }

  .sudoku-grid {
    --cell-size: min(34px, calc((100vw - 40px) / 9));
    padding: 4px;
  }

  .sudoku-input {
    font-size: 15px;
  }

  .side-block {
    padding: 8px;
  }

  .side-block h2 {
    font-size: 14px;
  }

  .side-text {
    font-size: 12px;
  }

  .bulk-input {
    font-size: 12px;
    padding: 6px 8px;
  }

  .status-bar {
    font-size: 12px;
    padding: 6px 8px;
  }

  .btn {
    font-size: 12px;
    padding: 6px 12px;
  }

  .btn.small {
    font-size: 11px;
    padding: 4px 8px;
  }
}

@media (max-width: 400px) {
  .sudoku-grid {
    --cell-size: min(32px, calc((100vw - 32px) / 9));
  }

  .sudoku-input {
    font-size: 14px;
  }

  .play-toolbar-row {
    flex-direction: column;
  }

  .level-select-wrapper,
  .play-btn,
  .play-timer-wrapper {
    width: 100%;
  }

  .level-select,
  .play-btn {
    width: 100%;
  }
}