* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Segoe UI', Arial, sans-serif;
    background: var(--bg-gradient);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
}

.container {
    display: flex;
    gap: 30px;
    max-width: 1200px;
    width: 100%;
    margin: 0 auto;
}

.game-section {
    flex: 1;
    max-width: 500px;
    background: var(--container-bg);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 30px;
    box-shadow: var(--container-shadow);
}

.info-section {
    width: 300px;
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.header {
    margin-bottom: 40px;
}

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

h1 {
    font-size: 80px;
    font-weight: bold;
    color: #fff;
    text-shadow: 0 0 10px rgba(255, 255, 255, 0.3);
    margin: 0;
}

.score-container {
    display: flex;
    gap: 15px;
}

.score-box {
    background: rgba(255, 255, 255, 0.15);
    padding: 15px 25px;
    border-radius: 15px;
    color: white;
    min-width: 120px;
    text-align: center;
    backdrop-filter: blur(5px);
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
    transition: transform 0.2s;
}

.score-box:hover {
    transform: translateY(-2px);
}

.score-label {
    font-size: 14px;
    display: block;
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: 5px;
}

#score, #best-score {
    font-size: 24px;
    font-weight: bold;
}

.controls {
    margin-bottom: 25px;
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
}

button {
    background: var(--button-gradient);
    color: white;
    border: none;
    padding: 12px 25px;
    border-radius: 12px;
    cursor: pointer;
    font-weight: bold;
    font-size: 16px;
    transition: all 0.3s ease;
    text-transform: uppercase;
    letter-spacing: 1px;
    box-shadow: var(--button-shadow);
    display: flex;
    align-items: center;
    gap: 8px;
}

button:hover {
    transform: translateY(-2px);
    box-shadow: var(--button-shadow);
    filter: brightness(1.1);
}

button:active {
    transform: translateY(1px);
}

button i {
    font-size: 18px;
}

.game-intro, .instructions {
    color: rgba(255, 255, 255, 0.8);
    margin-bottom: 15px;
    line-height: 1.6;
    font-size: 16px;
}

.game-container {
    background: rgba(255, 255, 255, 0.1);
    padding: 20px;
    border-radius: 20px;
    position: relative;
    margin-top: 20px;
    user-select: none;
    backdrop-filter: blur(5px);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
    aspect-ratio: 1;
}

.grid-container {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 15px;
    position: relative;
    border-radius: 12px;
    padding-bottom: 100%;
    background: rgba(255, 255, 255, 0.1);
    width: 100%;
    height: 0;
}

.grid-cell {
    position: absolute;
    width: calc(25% - 11.25px);
    height: calc(25% - 11.25px);
    background: rgba(255, 255, 255, 0.1);
    border-radius: 12px;
    transition: all 0.15s ease-in-out;
}

/* Position grid cells with correct spacing */
.grid-cell:nth-child(1) { left: 0; top: 0; }
.grid-cell:nth-child(2) { left: calc(25% + 3.75px); top: 0; }
.grid-cell:nth-child(3) { left: calc(50% + 7.5px); top: 0; }
.grid-cell:nth-child(4) { left: calc(75% + 11.25px); top: 0; }

.grid-cell:nth-child(5) { left: 0; top: calc(25% + 3.75px); }
.grid-cell:nth-child(6) { left: calc(25% + 3.75px); top: calc(25% + 3.75px); }
.grid-cell:nth-child(7) { left: calc(50% + 7.5px); top: calc(25% + 3.75px); }
.grid-cell:nth-child(8) { left: calc(75% + 11.25px); top: calc(25% + 3.75px); }

.grid-cell:nth-child(9) { left: 0; top: calc(50% + 7.5px); }
.grid-cell:nth-child(10) { left: calc(25% + 3.75px); top: calc(50% + 7.5px); }
.grid-cell:nth-child(11) { left: calc(50% + 7.5px); top: calc(50% + 7.5px); }
.grid-cell:nth-child(12) { left: calc(75% + 11.25px); top: calc(50% + 7.5px); }

.grid-cell:nth-child(13) { left: 0; top: calc(75% + 11.25px); }
.grid-cell:nth-child(14) { left: calc(25% + 3.75px); top: calc(75% + 11.25px); }
.grid-cell:nth-child(15) { left: calc(50% + 7.5px); top: calc(75% + 11.25px); }
.grid-cell:nth-child(16) { left: calc(75% + 11.25px); top: calc(75% + 11.25px); }

.tile {
    position: absolute;
    width: 100%;
    height: 100%;
    border-radius: 12px;
    font-weight: bold;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: all 0.15s ease-in-out;
    transform: scale(1);
    z-index: 1;
    box-shadow: var(--container-shadow);
}

.tile span {
    font-size: 32px;
    color: #fff;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

.tile-2 { background: linear-gradient(135deg, #ff6b6b 0%, #ff8e8e 100%); }
.tile-4 { background: linear-gradient(135deg, #ff9f43 0%, #ffbe76 100%); }
.tile-8 { background: linear-gradient(135deg, #ff6b81 0%, #ff4757 100%); }
.tile-16 { background: linear-gradient(135deg, #ff4757 0%, #ff6348 100%); }
.tile-32 { background: linear-gradient(135deg, #ff6348 0%, #ff7f50 100%); }
.tile-64 { background: linear-gradient(135deg, #ff7f50 0%, #ffa502 100%); }
.tile-128 { background: linear-gradient(135deg, #ffa502 0%, #ffbe76 100%); font-size: 28px; }
.tile-256 { background: linear-gradient(135deg, #ffbe76 0%, #ffd700 100%); font-size: 28px; }
.tile-512 { background: linear-gradient(135deg, #ffd700 0%, #ffa502 100%); font-size: 28px; }
.tile-1024 { background: linear-gradient(135deg, #ffa502 0%, #ff7f50 100%); font-size: 24px; }
.tile-2048 { background: linear-gradient(135deg, #ff7f50 0%, #ff6348 100%); font-size: 24px; }

.game-message {
    display: none;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.85);
    backdrop-filter: blur(5px);
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    border-radius: 20px;
    color: white;
    z-index: 100;
}

.game-message.active {
    display: flex;
    animation: fadeIn 0.3s ease-in-out;
}

.game-message p {
    font-size: 36px;
    font-weight: bold;
    margin-bottom: 25px;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

@media (max-width: 520px) {
    .container {
        padding: 10px;
    }

    .game-section {
        padding: 15px;
    }

    .info-section {
        padding: 15px;
    }

    h1 {
        font-size: 40px;
    }

    .score-box {
        padding: 10px 15px;
        min-width: 90px;
    }

    .controls {
        flex-direction: column;
    }

    button {
        width: 100%;
        justify-content: center;
    }

    .tile span {
        font-size: 24px;
    }

    .game-message p {
        font-size: 28px;
    }
}

@media (max-width: 1200px) {
    .container {
        flex-direction: column;
        align-items: center;
    }

    .info-section {
        width: 100%;
        max-width: 500px;
    }

    .game-section {
        margin-bottom: 20px;
    }

    .sidebar {
        position: static;
        transform: none;
        margin-top: 30px;
        width: 100%;
        max-width: 500px;
        margin: 20px auto 0;
    }

    .controls {
        justify-content: center;
    }

    button {
        padding: 10px 20px;
        font-size: 14px;
    }

    button i {
        font-size: 16px;
    }
}

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

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

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.tile-new {
    animation: pop 0.3s ease-in-out;
}

.tile-merged {
    z-index: 2;
    animation: merge 0.3s ease-in-out;
}

.pulse {
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); }
}

/* Add styles for new features */
.sidebar {
    position: fixed;
    right: 20px;
    top: 50%;
    transform: translateY(-50%);
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    padding: 20px;
    border-radius: 20px;
    display: flex;
    flex-direction: column;
    gap: 15px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
    z-index: 90;
}

.theme-switcher {
    display: flex;
    gap: 10px;
    margin-bottom: 15px;
    justify-content: center;
}

.theme-option {
    width: 30px;
    height: 30px;
    border-radius: 50%;
    cursor: pointer;
    border: 2px solid transparent;
    transition: all 0.3s ease;
}

.theme-option.theme-dark {
    background: linear-gradient(135deg, #1e1e2e 0%, #2d2d44 100%);
}

.theme-option.theme-light {
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
}

.theme-option.theme-neon {
    background: linear-gradient(135deg, #000428 0%, #004e92 100%);
}

.theme-option.active {
    border-color: var(--accent-color);
    transform: scale(1.1);
}

.leaderboard {
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    padding: 20px;
    border-radius: 15px;
    margin-top: 20px;
}

.leaderboard-title {
    font-size: 18px;
    font-weight: bold;
    margin-bottom: 15px;
    text-align: center;
}

.leaderboard-entry {
    display: flex;
    justify-content: space-between;
    padding: 8px 0;
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.help-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.9);
    backdrop-filter: blur(5px);
    display: none;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.help-content {
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    padding: 30px;
    border-radius: 20px;
    max-width: 600px;
    width: 90%;
    color: white;
}

.shortcut-list {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 15px;
    margin-top: 20px;
}

.shortcut-item {
    display: flex;
    align-items: center;
    gap: 10px;
}

.key {
    background: rgba(255, 255, 255, 0.2);
    padding: 5px 10px;
    border-radius: 5px;
    font-family: monospace;
}

.stats-container {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 15px;
    margin-top: 20px;
}

.stat-box {
    background: rgba(255, 255, 255, 0.1);
    padding: 15px;
    border-radius: 12px;
    text-align: center;
}

.stat-value {
    font-size: 24px;
    font-weight: bold;
    margin-bottom: 5px;
}

.stat-label {
    font-size: 14px;
    opacity: 0.8;
}

/* Theme variables */
.theme-dark {
    --bg-gradient: linear-gradient(135deg, #1e1e2e 0%, #2d2d44 100%);
    --text-color: #ffffff;
    --container-bg: rgba(255, 255, 255, 0.1);
    --container-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
    --accent-color: #ff6b6b;
    --button-gradient: linear-gradient(135deg, #ff6b6b 0%, #ff8e8e 100%);
    --button-shadow: 0 4px 15px rgba(255, 107, 107, 0.3);
}

.theme-light {
    --bg-gradient: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    --text-color: #776e65;
    --container-bg: rgba(255, 255, 255, 0.9);
    --container-shadow: 0 8px 32px rgba(0, 0, 0, 0.05);
    --accent-color: #ff9f43;
    --button-gradient: linear-gradient(135deg, #ff9f43 0%, #ffbe76 100%);
    --button-shadow: 0 4px 15px rgba(255, 159, 67, 0.3);
}

.theme-neon {
    --bg-gradient: linear-gradient(135deg, #000428 0%, #004e92 100%);
    --text-color: #ffffff;
    --container-bg: rgba(0, 0, 0, 0.5);
    --container-shadow: 0 8px 32px rgba(0, 255, 135, 0.2);
    --accent-color: #00ff87;
    --button-gradient: linear-gradient(135deg, #00ff87 0%, #60efff 100%);
    --button-shadow: 0 4px 15px rgba(0, 255, 135, 0.3);
}

.theme-dark .tile-2 { background: linear-gradient(135deg, #ff6b6b 0%, #ff8e8e 100%); }
.theme-dark .tile-4 { background: linear-gradient(135deg, #ff9f43 0%, #ffbe76 100%); }
.theme-dark .tile-8 { background: linear-gradient(135deg, #ff6b81 0%, #ff4757 100%); }
.theme-dark .tile-16 { background: linear-gradient(135deg, #ff4757 0%, #ff6348 100%); }
.theme-dark .tile-32 { background: linear-gradient(135deg, #ff6348 0%, #ff7f50 100%); }
.theme-dark .tile-64 { background: linear-gradient(135deg, #ff7f50 0%, #ffa502 100%); }
.theme-dark .tile-128 { background: linear-gradient(135deg, #ffa502 0%, #ffbe76 100%); }
.theme-dark .tile-256 { background: linear-gradient(135deg, #ffbe76 0%, #ffd700 100%); }
.theme-dark .tile-512 { background: linear-gradient(135deg, #ffd700 0%, #ffa502 100%); }
.theme-dark .tile-1024 { background: linear-gradient(135deg, #ffa502 0%, #ff7f50 100%); }
.theme-dark .tile-2048 { background: linear-gradient(135deg, #ff7f50 0%, #ff6348 100%); }

.theme-light .tile-2 { background: linear-gradient(135deg, #f67280 0%, #f8b195 100%); }
.theme-light .tile-4 { background: linear-gradient(135deg, #f8b195 0%, #ffd3b6 100%); }
.theme-light .tile-8 { background: linear-gradient(135deg, #00b894 0%, #00cec9 100%); }
.theme-light .tile-16 { background: linear-gradient(135deg, #00cec9 0%, #81ecec 100%); }
.theme-light .tile-32 { background: linear-gradient(135deg, #74b9ff 0%, #a3d8f4 100%); }
.theme-light .tile-64 { background: linear-gradient(135deg, #6c5ce7 0%, #a29bfe 100%); }
.theme-light .tile-128 { background: linear-gradient(135deg, #fd79a8 0%, #fab1a0 100%); }
.theme-light .tile-256 { background: linear-gradient(135deg, #e84393 0%, #fd79a8 100%); }
.theme-light .tile-512 { background: linear-gradient(135deg, #6c5ce7 0%, #81ecec 100%); }
.theme-light .tile-1024 { background: linear-gradient(135deg, #00b894 0%, #81ecec 100%); }
.theme-light .tile-2048 { background: linear-gradient(135deg, #e84393 0%, #a29bfe 100%); }

.theme-neon .tile-2 { background: linear-gradient(135deg, #00ff87 0%, #60efff 100%); }
.theme-neon .tile-4 { background: linear-gradient(135deg, #0061ff 0%, #60efff 100%); }
.theme-neon .tile-8 { background: linear-gradient(135deg, #ff00ff 0%, #ff73ff 100%); }
.theme-neon .tile-16 { background: linear-gradient(135deg, #00ff00 0%, #73ff73 100%); }
.theme-neon .tile-32 { background: linear-gradient(135deg, #ff3131 0%, #ff7373 100%); }
.theme-neon .tile-64 { background: linear-gradient(135deg, #00ffff 0%, #73ffff 100%); }
.theme-neon .tile-128 { background: linear-gradient(135deg, #ff00ff 0%, #ff73ff 100%); }
.theme-neon .tile-256 { background: linear-gradient(135deg, #ffff00 0%, #ffff73 100%); }
.theme-neon .tile-512 { background: linear-gradient(135deg, #00ff87 0%, #60efff 100%); }
.theme-neon .tile-1024 { background: linear-gradient(135deg, #ff00ff 0%, #00ffff 100%); }
.achievements {
    background: var(--container-bg);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 20px;
    box-shadow: var(--container-shadow);
}

.achievements-title {
    font-size: 18px;
    font-weight: bold;
    margin-bottom: 15px;
    text-align: center;
    color: var(--text-color);
}

.achievement-item {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 10px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 10px;
    margin-bottom: 10px;
    transition: all 0.3s ease;
}

.achievement-item.unlocked {
    background: var(--accent-color);
    color: #fff;
}

.achievement-icon {
    font-size: 24px;
    opacity: 0.5;
}

.achievement-item.unlocked .achievement-icon {
    opacity: 1;
}

/* Responsive design for new features */
@media (max-width: 1200px) {
    .sidebar {
        position: static;
        transform: none;
        margin-top: 30px;
        width: 100%;
    }
}