:root {
    --bg-color: #0F172A;
    --text-color: #F8FAFC;
    --grid-bg: rgba(255, 255, 255, 0.05);
    --cell-bg: rgba(255, 255, 255, 0.1);
    --glass-bg: rgba(255, 255, 255, 0.03);
    --glass-border: rgba(255, 255, 255, 0.08);
    --primary-gradient: linear-gradient(135deg, #3B82F6 0%, #8B5CF6 100%);
    --primary-hover: linear-gradient(135deg, #2563EB 0%, #7C3AED 100%);
    
    --tile-color-text-dark: #1E293B;
    --tile-color-text-light: #F8FAFC;
    
    /* Tile Background Colors - vibrant and premium */
    --color-2: #E2E8F0;
    --color-4: #CBD5E1;
    --color-8: #F59E0B;
    --color-16: #F97316;
    --color-32: #EF4444;
    --color-64: #EC4899;
    --color-128: #EAB308;
    --color-256: #EAB308;
    --color-512: #EAB308;
    --color-1024: #EAB308;
    --color-2048: #EAB308;
    --color-super: #3B82F6; /* Fallback for > 2048 */
    
    /* Box shadows for higher tiles to make them glow */
    --glow-128: 0 0 20px rgba(234, 179, 8, 0.3);
    --glow-256: 0 0 25px rgba(234, 179, 8, 0.4);
    --glow-512: 0 0 30px rgba(234, 179, 8, 0.5);
    --glow-1024: 0 0 35px rgba(234, 179, 8, 0.6);
    --glow-2048: 0 0 40px rgba(234, 179, 8, 0.8);
    
    --grid-spacing: 12px;
    --grid-size: 400px;
    --cell-size: calc((var(--grid-size) - var(--grid-spacing) * 5) / 4);
    
    --transition-speed: 150ms;
}

@media (max-width: 480px) {
    :root {
        --grid-size: 90vw; /* Responsive grid for mobile */
        --grid-spacing: 8px;
    }
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    user-select: none; /* Prevent selection */
    -webkit-tap-highlight-color: transparent;
}

body {
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: 'Outfit', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    overflow: hidden;
    touch-action: none; /* Prevent pull-to-refresh and zooming on mobile */
}

.container {
    width: var(--grid-size);
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 20px;
    padding-bottom: 50px;
}

header {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

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

.title {
    font-size: 3.5rem;
    font-weight: 800;
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    letter-spacing: -2px;
}

.scores-container {
    display: flex;
    gap: 10px;
}

.score-box {
    background: var(--glass-bg);
    border: 1px solid var(--glass-border);
    border-radius: 12px;
    padding: 8px 20px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-width: 80px;
    backdrop-filter: blur(10px);
}

.score-title {
    font-size: 0.75rem;
    font-weight: 600;
    color: #94A3B8;
    text-transform: uppercase;
    letter-spacing: 1px;
}

.score-value {
    font-size: 1.5rem;
    font-weight: 800;
}

.game-intro {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 1.1rem;
    color: #CBD5E1;
}

.restart-button, .retry-button {
    background: var(--primary-gradient);
    color: white;
    border: none;
    border-radius: 8px;
    padding: 12px 20px;
    font-family: inherit;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: transform 0.2s, opacity 0.2s;
    box-shadow: 0 4px 15px rgba(59, 130, 246, 0.3);
}

.restart-button:active, .retry-button:active {
    transform: scale(0.95);
}

.restart-button:hover, .retry-button:hover {
    opacity: 0.9;
}

.game-container {
    position: relative;
    background: var(--grid-bg);
    border: 1px solid var(--glass-border);
    border-radius: 16px;
    padding: var(--grid-spacing);
    width: var(--grid-size);
    height: var(--grid-size);
    backdrop-filter: blur(20px);
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.4);
}

.game-message {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(15, 23, 42, 0.8);
    backdrop-filter: blur(5px);
    z-index: 100;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    border-radius: 16px;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s ease;
}

.game-message.game-over, .game-message.game-won {
    opacity: 1;
    pointer-events: auto;
}

.game-message p {
    font-size: 3rem;
    font-weight: 800;
    margin-bottom: 20px;
}

.game-message.game-won p {
    background: linear-gradient(135deg, #FBBF24 0%, #F59E0B 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.grid-container {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(4, 1fr);
    gap: var(--grid-spacing);
    width: 100%;
    height: 100%;
}

.grid-cell {
    width: 100%;
    height: 100%;
    background: var(--cell-bg);
    border-radius: 8px;
}

.tile-container {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 10;
    pointer-events: none;
}

.tile {
    position: absolute;
    width: var(--cell-size);
    height: var(--cell-size);
    border-radius: 8px;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 2.5rem;
    font-weight: 800;
    transition: transform var(--transition-speed) ease-in-out, 
                opacity var(--transition-speed) ease-in-out,
                background-color var(--transition-speed) ease-in-out,
                top var(--transition-speed) ease-in-out,
                left var(--transition-speed) ease-in-out;
    transform-origin: center center;
}

/* Animations */
@keyframes pop {
    0% { transform: scale(0); }
    50% { transform: scale(1.1); }
    100% { transform: scale(1); }
}

@keyframes merge {
    0% { transform: scale(1); }
    50% { transform: scale(1.2); }
    100% { transform: scale(1); }
}

.tile.new {
    animation: pop 0.2s ease forwards;
}

.tile.merged {
    animation: merge 0.2s ease forwards;
    z-index: 20;
}

/* Dynamic positioning classes will be handled via JS style setting */

/* Tile colors */
.tile-2 { background-color: var(--color-2); color: var(--tile-color-text-dark); }
.tile-4 { background-color: var(--color-4); color: var(--tile-color-text-dark); }
.tile-8 { background-color: var(--color-8); color: var(--tile-color-text-light); }
.tile-16 { background-color: var(--color-16); color: var(--tile-color-text-light); }
.tile-32 { background-color: var(--color-32); color: var(--tile-color-text-light); }
.tile-64 { background-color: var(--color-64); color: var(--tile-color-text-light); }
.tile-128 { background-color: var(--color-128); color: var(--tile-color-text-light); box-shadow: var(--glow-128); font-size: 2rem;}
.tile-256 { background-color: var(--color-256); color: var(--tile-color-text-light); box-shadow: var(--glow-256); font-size: 2rem;}
.tile-512 { background-color: var(--color-512); color: var(--tile-color-text-light); box-shadow: var(--glow-512); font-size: 2rem;}
.tile-1024 { background-color: var(--color-1024); color: var(--tile-color-text-light); box-shadow: var(--glow-1024); font-size: 1.5rem;}
.tile-2048 { background-color: var(--color-2048); color: var(--tile-color-text-light); box-shadow: var(--glow-2048); font-size: 1.5rem;}
.tile-super { background-color: var(--color-super); color: var(--tile-color-text-light); box-shadow: 0 0 50px rgba(59, 130, 246, 0.8); font-size: 1.2rem;}

/* Adjust font sizes for mobile slightly */
@media (max-width: 480px) {
    .tile { font-size: 2rem; }
    .tile-128, .tile-256, .tile-512 { font-size: 1.6rem; }
    .tile-1024, .tile-2048 { font-size: 1.2rem; }
}