/* ==========================================================================
   1. CSS Variables & Theme Setup
   ========================================================================== */
:root {
  /* Light Mode Colors (Default) */
  --bg-color: #f8f9fa;
  --panel-bg: #ffffff;
  --text-color: #212529;
  --primary-color: #4a90e2;
  --primary-hover: #357abd;
  --secondary-color: #6c757d;
  --secondary-hover: #5a6268;
  --danger-color: #e74c3c;
  --danger-hover: #c0392b;
  --toggle-active: #f39c12;
  --border-color: #cccccc;
  --thick-border-color: #333333;
  --cell-selected: #d0e1fd;
  --cell-hover: #e8f0fe;
  --cell-correct: #d4edda;
  --text-correct: #155724;
  --cell-incorrect: #f8d7da;
  --text-incorrect: #721c24;
  --note-color: #7f8c8d;
  --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

body.dark-mode {
  /* Dark Mode Overrides */
  --bg-color: #121212;
  --panel-bg: #1e1e1e;
  --text-color: #e0e0e0;
  --primary-color: #3700b3;
  --primary-hover: #6200ee;
  --secondary-color: #03dac6;
  --secondary-hover: #018786;
  --border-color: #444444;
  --thick-border-color: #ffffff;
  --cell-selected: #2c3e50;
  --cell-hover: #2a2a2a;
  --cell-correct: #1b4332;
  --text-correct: #d4edda;
  --cell-incorrect: #621708;
  --text-incorrect: #f8d7da;
  --note-color: #a0a0a0;
  --shadow: 0 4px 6px rgba(0, 0, 0, 0.5);
}

/* ==========================================================================
   2. Base & Layout Styles
   ========================================================================== */
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-color);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 20px;
  transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
  background-color: var(--panel-bg);
  padding: 25px;
  border-radius: 12px;
  box-shadow: var(--shadow);
  max-width: 500px;
  width: 100%;
}

header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
}

h1 {
  font-size: 2rem;
}

/* Button UI Elements */
.btn {
  padding: 8px 16px;
  border: none;
  border-radius: 6px;
  font-weight: 600;
  cursor: pointer;
  transition: background-color 0.2s ease, transform 0.1s ease;
}

.btn:active {
  transform: scale(0.97);
}

.btn.primary {
  background-color: var(--primary-color);
  color: #fff;
}
.btn.primary:hover {
  background-color: var(--primary-hover);
}

.btn.secondary {
  background-color: var(--secondary-color);
  color: #fff;
}
.btn.secondary:hover {
  background-color: var(--secondary-hover);
}

.btn.danger {
  background-color: var(--danger-color);
  color: #fff;
}
.btn.danger:hover {
  background-color: var(--danger-hover);
}

.btn.toggle {
  background-color: var(--secondary-color);
  color: #fff;
}
.btn.toggle.active {
  background-color: var(--toggle-active);
}

/* ==========================================================================
   3. Game Controls
   ========================================================================== */
.game-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
  gap: 10px;
  flex-wrap: wrap;
}

.control-group {
  display: flex;
  align-items: center;
  gap: 8px;
}

select {
  padding: 6px 12px;
  border-radius: 6px;
  border: 1px solid var(--border-color);
  background-color: var(--panel-bg);
  color: var(--text-color);
  outline: none;
}

/* ==========================================================================
   4. Sudoku Grid Layout
   ========================================================================== */
.board-container {
  display: flex;
  justify-content: center;
  margin-bottom: 20px;
}

.board {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  grid-template-rows: repeat(9, 1fr);
  width: 100%;
  aspect-ratio: 1 / 1;
  border: 3px solid var(--thick-border-color);
}

.cell {
  border: 1px solid var(--border-color);
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 1.5rem;
  font-weight: bold;
  cursor: pointer;
  user-select: none;
  position: relative;
  transition: background-color 0.2s ease;
}

/* Thicker borders for the 3x3 grids */
.cell[data-col="2"], .cell[data-col="5"] {
  border-right: 2.5px solid var(--thick-border-color);
}
.cell[data-row="2"], .cell[data-row="5"] {
  border-bottom: 2.5px solid var(--thick-border-color);
}

/* Cell States */
.cell:hover {
  background-color: var(--cell-hover);
}

.cell.selected {
  background-color: var(--cell-selected) !important;
}

.cell.given {
  color: var(--text-color);
  font-weight: 800;
  cursor: not-allowed;
}

.cell.correct {
  background-color: var(--cell-correct);
  color: var(--text-correct);
}

.cell.incorrect {
  background-color: var(--cell-incorrect);
  color: var(--text-incorrect);
}

/* 3x3 Notes Grid Inside Empty Cells */
.notes-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  pointer-events: none;
}

.notes-grid span {
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 0.65rem;
  font-weight: 600;
  color: var(--note-color);
}

/* ==========================================================================
   5. Numpad & Controls
   ========================================================================== */
.numpad {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
  margin-bottom: 20px;
}

.num-btn {
  padding: 12px;
  font-size: 1.2rem;
  font-weight: bold;
  border-radius: 6px;
  border: 1px solid var(--border-color);
  background-color: var(--panel-bg);
  color: var(--text-color);
  cursor: pointer;
  transition: background-color 0.2s ease;
}

.num-btn:hover {
  background-color: var(--cell-hover);
}

#erase-btn {
  grid-column: span 1;
}

/* ==========================================================================
   6. Statistics Section
   ========================================================================== */
.stats-board {
  border-top: 1px solid var(--border-color);
  padding-top: 15px;
}

.stats-board h2 {
  font-size: 1.1rem;
  margin-bottom: 10px;
  text-align: center;
}

.stats-grid {
  display: flex;
  justify-content: space-around;
  text-align: center;
}

.stat-box {
  display: flex;
  flex-direction: column;
}

.stat-label {
  font-size: 0.8rem;
  color: var(--secondary-color);
}

.stat-value {
  font-size: 1.3rem;
  font-weight: bold;
}