/* ========================================
   CSS Custom Properties (Theming)
   ======================================== */
:root {
    /* Colors */
    --color-primary: #2563eb;
    --color-primary-hover: #1d4ed8;
    --color-success: #16a34a;
    --color-success-hover: #15803d;
    --color-danger: #dc2626;
    --color-danger-hover: #b91c1c;
    --color-accent: #7c3aed;
    --color-accent-hover: #6d28d9;

    /* Neutrals */
    --color-bg: #f0fdf4;
    --color-surface: #ffffff;
    --color-border: #d1d5db;
    --color-text: #1f2937;
    --color-text-muted: #6b7280;

    /* Grid colors */
    --color-grid-lines: #e5e7eb;
    --color-cell-alive: #1f2937;
    --color-cell-dead: #ffffff;

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;

    /* Typography */
    --font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI',
                   Roboto, Oxygen, Ubuntu, sans-serif;
    --font-mono: 'Courier New', Courier, monospace;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.25rem;
    --font-size-xl: 1.5rem;

    /* Borders & Shadows */
    --border-radius: 0.5rem;
    --border-radius-sm: 0.25rem;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);

    /* Transitions */
    --transition-fast: 150ms ease;
}

/* ========================================
   Reset & Base Styles
   ======================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.5;
    color: var(--color-text);
    background-color: var(--color-bg);
    min-height: 100vh;
}

/* Accessibility: Screen reader only text */
.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* ========================================
   Layout
   ======================================== */
.app-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-lg);
}

.app-header {
    text-align: center;
    margin-bottom: var(--spacing-lg);
}

.app-header h1 {
    font-family: var(--font-mono);
    font-size: var(--font-size-xl);
    color: var(--color-text);
}

.game-layout {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
}

@media (min-width: 1024px) {
    .game-layout {
        grid-template-columns: auto 320px;
        align-items: start;
    }
}

/* ========================================
   Canvas Section
   ======================================== */
.canvas-section {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.canvas-wrapper {
    background: var(--color-surface);
    border-radius: var(--border-radius);
    padding: var(--spacing-md);
    box-shadow: var(--shadow-md);
    display: flex;
    justify-content: center;
    overflow: auto;
}

#game-canvas {
    border: 1px solid var(--color-border);
    cursor: crosshair;
    max-width: 100%;
    height: auto;
}

.game-stats {
    text-align: center;
}

.cycle-counter {
    font-family: var(--font-mono);
    font-size: var(--font-size-lg);
    color: var(--color-text);
    background: var(--color-surface);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--border-radius-sm);
    box-shadow: var(--shadow-sm);
}

/* ========================================
   Controls Section
   ======================================== */
.controls-section {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.panel {
    background: var(--color-surface);
    border-radius: var(--border-radius);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
}

.panel h2 {
    font-size: var(--font-size-lg);
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-sm);
    border-bottom: 2px solid var(--color-border);
}

/* Rules List */
.rules-list {
    list-style: none;
    padding-left: 0;
}

.rules-list li {
    position: relative;
    padding-left: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
    font-size: var(--font-size-sm);
    color: var(--color-text-muted);
}

.rules-list li::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0.5em;
    width: 8px;
    height: 8px;
    background: var(--color-cell-alive);
    border-radius: 50%;
}

/* Control Groups */
.control-group {
    display: flex;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
}

.control-group input {
    flex: 1;
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius-sm);
    font-size: var(--font-size-base);
}

.control-group input:focus {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

.button-group {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
}

/* ========================================
   Buttons
   ======================================== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: var(--font-size-base);
    font-weight: 500;
    text-decoration: none;
    border: none;
    border-radius: var(--border-radius-sm);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn:focus {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

.btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.btn-full {
    width: 100%;
}

.btn-primary {
    background: var(--color-primary);
    color: white;
}
.btn-primary:hover:not(:disabled) {
    background: var(--color-primary-hover);
}

.btn-success {
    background: var(--color-success);
    color: white;
}
.btn-success:hover:not(:disabled) {
    background: var(--color-success-hover);
}

.btn-danger {
    background: var(--color-danger);
    color: white;
}
.btn-danger:hover:not(:disabled) {
    background: var(--color-danger-hover);
}

.btn-accent {
    background: var(--color-accent);
    color: white;
}
.btn-accent:hover:not(:disabled) {
    background: var(--color-accent-hover);
}

.btn-secondary {
    background: var(--color-border);
    color: var(--color-text);
}
.btn-secondary:hover:not(:disabled) {
    background: #9ca3af;
}

.btn-outline {
    background: transparent;
    color: var(--color-primary);
    border: 1px solid var(--color-primary);
}
.btn-outline:hover:not(:disabled) {
    background: var(--color-primary);
    color: white;
}

/* Play/Stop state */
.btn-playing {
    background: var(--color-danger);
}
.btn-playing:hover:not(:disabled) {
    background: var(--color-danger-hover);
}

/* ========================================
   Modal (Native Dialog)
   ======================================== */
.modal {
    border: none;
    border-radius: var(--border-radius);
    padding: 0;
    max-width: 500px;
    width: 90%;
    box-shadow: var(--shadow-lg);
}

.modal::backdrop {
    background: rgba(0, 0, 0, 0.5);
}

.modal-content {
    padding: 0;
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-lg);
    border-bottom: 1px solid var(--color-border);
}

.modal-header h2 {
    margin: 0;
    font-size: var(--font-size-lg);
    border: none;
    padding: 0;
}

.btn-close {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    padding: var(--spacing-xs);
    line-height: 1;
    color: var(--color-text-muted);
}

.btn-close:hover {
    color: var(--color-text);
}

.modal-body {
    padding: var(--spacing-lg);
}

.modal-body p {
    margin-bottom: var(--spacing-md);
}

.modal-body p:last-child {
    margin-bottom: 0;
}

.modal-body a {
    color: var(--color-primary);
}

.modal-footer {
    padding: var(--spacing-lg);
    border-top: 1px solid var(--color-border);
    text-align: right;
}

/* ========================================
   Links Panel
   ======================================== */
.links-panel {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

/* ========================================
   Responsive Adjustments
   ======================================== */
@media (max-width: 640px) {
    .app-container {
        padding: var(--spacing-md);
    }

    .canvas-wrapper {
        padding: var(--spacing-sm);
    }

    #game-canvas {
        width: 100%;
        height: auto;
    }
}