/* CSS Variables for theming */
:root {
    --primary-color: #1976D2;
    --primary-dark: #1565C0;
    --primary-light: #BBDEFB;
    --secondary-color: #424242;
    --surface-color: #FFFFFF;
    --background-color: #F5F5F5;
    --on-surface: #212121;
    --on-background: #212121;
    --on-primary: #FFFFFF;
    --error-color: #D32F2F;
    --error-light: #FFCDD2;
    --success-color: #388E3C;
    --shadow-color: rgba(0, 0, 0, 0.12);
    --shadow-color-dark: rgba(0, 0, 0, 0.24);
    --border-color: #E0E0E0;
    --disabled-color: #9E9E9E;
}

[data-theme="dark"] {
    --primary-color: #2196F3;
    --primary-dark: #1976D2;
    --primary-light: #64B5F6;
    --secondary-color: #757575;
    --surface-color: #424242;
    --background-color: #303030;
    --on-surface: #FFFFFF;
    --on-background: #FFFFFF;
    --on-primary: #000000;
    --error-color: #F44336;
    --error-light: #E57373;
    --success-color: #4CAF50;
    --shadow-color: rgba(0, 0, 0, 0.3);
    --shadow-color-dark: rgba(0, 0, 0, 0.5);
    --border-color: #616161;
    --disabled-color: #757575;
}

* {
    box-sizing: border-box;
}

body {
    font-family: 'Roboto', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    margin: 0;
    padding: 0;
    background-color: var(--background-color);
    color: var(--on-background);
    transition: background-color 0.3s ease, color 0.3s ease;
    min-height: 100vh;
    overflow-x: hidden;
}

/* Material Design App Bar */
.app-bar {
    position: sticky;
    top: 0;
    z-index: 100;
    background-color: var(--primary-color);
    color: var(--on-primary);
    box-shadow: 0 2px 4px var(--shadow-color);
    transition: background-color 0.3s ease;
}

.app-bar-content {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 16px;
    height: 56px;
    max-width: 1200px;
    margin: 0 auto;
}

.app-title {
    font-size: 20px;
    font-weight: 500;
    margin: 0;
    letter-spacing: 0.15px;
}

.app-bar-actions {
    display: flex;
    align-items: center;
    gap: 16px;
}

.timer {
    font-size: 18px;
    font-weight: 500;
    font-variant-numeric: tabular-nums;
    letter-spacing: 1px;
}

.icon-button {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    border: none;
    border-radius: 50%;
    background-color: transparent;
    color: var(--on-primary);
    cursor: pointer;
    transition: background-color 0.3s ease;
}
.icon-button:hover {
    background-color: rgba(255, 255, 255, 0.1);
}
.icon-button:active {
    background-color: rgba(255, 255, 255, 0.2);
}
.icon {
    width: 24px;
    height: 24px;
    fill: currentColor;
}

/* Main Content */
.main-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 16px;
}

/* Material Design Cards */
.controls-card,
.game-card,
.rules-card {
    background-color: var(--surface-color);
    border-radius: 8px;
    box-shadow: 0 2px 4px var(--shadow-color);
    margin-bottom: 16px;
    transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

.controls-card {
    padding: 16px;
}
.game-card {
    padding: 24px;
}
.rules-card {
    padding: 24px;
}

/* Controls */
.controls {
    display: flex;
    gap: 16px;
    align-items: center;
    flex-wrap: wrap;
    justify-content: center;
}

.select-wrapper {
    position: relative;
}

.select-field {
    appearance: none;
    background-color: transparent;
    border: 2px solid var(--border-color);
    border-radius: 4px;
    padding: 12px 40px 12px 16px;
    font-size: 16px;
    color: var(--on-surface);
    cursor: pointer;
    transition: border-color 0.3s ease;
    min-width: 120px;
}
.select-field:focus {
    outline: none;
    border-color: var(--primary-color);
}
.select-field:hover {
    border-color: var(--primary-color);
}
.select-wrapper::after {
    content: '';
    position: absolute;
    right: 16px;
    top: 50%;
    transform: translateY(-50%);
    width: 0;
    height: 0;
    border-left: 6px solid transparent;
    border-right: 6px solid transparent;
    border-top: 6px solid var(--on-surface);
    pointer-events: none;
}

/* Material Design Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 12px 24px;
    border: none;
    border-radius: 4px;
    font-size: 14px;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.75px;
    cursor: pointer;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}
.btn-primary {
    background-color: var(--primary-color);
    color: var(--on-primary);
    box-shadow: 0 2px 4px var(--shadow-color);
}
.btn-primary:hover {
    background-color: var(--primary-dark);
    box-shadow: 0 4px 8px var(--shadow-color-dark);
}
.btn-secondary {
    background-color: transparent;
    color: var(--primary-color);
    border: 2px solid var(--primary-color);
}
.btn-secondary:hover {
    background-color: var(--primary-light);
}
.btn:active {
    transform: translateY(1px);
}
.btn-icon {
    width: 18px;
    height: 18px;
    fill: currentColor;
}

/* Game Board */
.board-container {
    display: flex;
    justify-content: center;
    flex-direction: column;
    align-items: center;
}

#status {
    margin-top: 16px;
    text-align: center;
    font-weight: 500;
    font-size: 16px;
    min-height: 24px;
}

#sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 1px;
    border: 2px solid var(--on-surface);
    width: 100%;
    max-width: 400px;
    aspect-ratio: 1;
    background-color: var(--on-surface);
    border-radius: 4px;
    overflow: hidden;
    box-shadow: 0 4px 8px var(--shadow-color);
    box-sizing: border-box;
}

.cell {
    display: flex;
    justify-content: center;
    align-items: center;
    width: 100%;
    aspect-ratio: 1;
    background-color: var(--surface-color);
    font-size: 24px;
    font-weight: 400;
    cursor: pointer;
    user-select: none;
    border: 1px solid var(--border-color);
    box-sizing: border-box;
    transition: all 0.2s ease;
    font-variant-numeric: tabular-nums;
}
.cell:hover {
    background-color: var(--primary-light);
}
.cell.selected {
    background-color: var(--primary-color);
    color: var(--on-primary);
}
.cell.initial {
    background-color: var(--background-color);
    font-weight: 500;
    cursor: not-allowed;
}
.cell.error {
    background-color: var(--error-light);
    color: var(--error-color);
}

/* Sudoku grid thick borders */
.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid var(--on-surface);
}
.cell:nth-child(3n) {
    border-right: 2px solid var(--on-surface);
}
.cell:nth-child(9n) {
    border-right: 1px solid var(--border-color);
}

/* Number Pad */
.number-pad {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    grid-gap: 8px;
    margin-top: 12px;
    max-width: 400px;
    width: 100%;
}
.number-btn {
    padding: 16px 8px;
    font-size: 18px;
    font-weight: 500;
    background-color: var(--surface-color);
    color: var(--on-surface);
    border: 2px solid var(--border-color);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 1px 3px var(--shadow-color);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 4px;
    min-height: 56px;
}
.number-btn:hover {
    background-color: var(--primary-light);
    border-color: var(--primary-color);
    box-shadow: 0 2px 6px var(--shadow-color-dark);
}
.number-btn:active {
    transform: scale(0.98);
}
.number-btn:disabled {
    background-color: var(--disabled-color);
    color: var(--surface-color);
    cursor: not-allowed;
    transform: none;
    border-color: var(--disabled-color);
}
.number-btn-clear {
    grid-column: span 1;
    border: none;
    background-color: transparent;
    box-shadow: none;
}
.number-btn-clear:hover {
    background-color: transparent;
    border: none;
    box-shadow: none;
}
.number-btn-clear svg {
    width: 24px;
    height: 24px;
    fill: #666666;
    transition: fill 0.3s ease;
}
.number-btn-clear:hover svg {
    fill: var(--primary-color);
}

/* Check button placement */
.check-button-container {
    margin-top: 16px;
    width: 100%;
    display: flex;
    justify-content: center;
}
.check-button-container .btn {
    width: 100%;
    max-width: 400px;
}

/* Rules Section */
.rules-card h2 {
    color: var(--primary-color);
    margin-top: 0;
    margin-bottom: 16px;
    font-size: 24px;
    font-weight: 500;
}
.rules-card p {
    line-height: 1.6;
    margin-bottom: 16px;
}
.rules-card ul {
    line-height: 1.6;
    padding-left: 24px;
}
.rules-card li {
    margin-bottom: 8px;
}

/* Save Indicator */
.save-indicator {
    position: fixed;
    top: 80px;
    right: 16px;
    background-color: var(--success-color);
    color: white;
    padding: 12px 16px;
    border-radius: 4px;
    font-size: 14px;
    font-weight: 500;
    opacity: 0;
    transition: opacity 0.3s ease;
    z-index: 1000;
    box-shadow: 0 4px 8px var(--shadow-color-dark);
}
.save-indicator.show {
    opacity: 1;
}

/* Responsive Design */
@media (max-width: 768px) {
    .main-content {
        padding: 8px;
    }
    .app-bar-content {
        padding: 0 12px;
    }
    .app-title {
        font-size: 18px;
    }
    .timer {
        font-size: 16px;
    }
    .controls {
        gap: 12px;
    }
    .btn {
        padding: 10px 16px;
        font-size: 13px;
    }
    #sudoku-board {
        max-width: 100%;
        width: 100%;
    }
    .cell {
        font-size: 24px;
    }
    .number-pad {
        max-width: 100%;
        width: 100%;
        grid-gap: 6px;
    }
    .number-btn {
        padding: 12px 6px;
        font-size: 16px;
        min-height: 48px;
    }
    .game-card,
    .controls-card,
    .rules-card {
        padding: 5px;
    }
}

@media (max-width: 480px) {
    .main-content {
        padding: 0;
    }
    .controls {
        flex-direction: column;
        align-items: stretch;
    }
    .btn {
        width: 100%;
        justify-content: center;
    }
    .select-field {
        width: 100%;
    }
    .app-bar-actions {
        gap: 8px;
    }
    .timer {
        font-size: 14px;
    }
    #sudoku-board {
        width: calc(100vw - 10px);
        max-width: calc(100vw - 10px);
        min-width: 0;
        margin-left: 5px;
        margin-right: 5px;
    }
    .number-pad {
        width: calc(100vw - 10px);
        max-width: calc(100vw - 10px);
        margin-left: 5px;
        margin-right: 5px;
    }
}


/* High contrast mode support */
@media (prefers-contrast: high) {
    .cell {
        border-width: 2px;
    }
    .btn {
        border-width: 2px;
    }
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}