:root {
    --field-width: min(500px, calc(100vw - 32px));
    --grid-spacing: 15px;
    --grid-row-cells: 4;
    --cell-size: calc((var(--field-width) - (var(--grid-spacing) * (var(--grid-row-cells) + 1))) / var(--grid-row-cells));
    
    --bg-color: #faf8ef;
    --grid-color: #bbada0;
    --empty-cell-color: #cdc1b4;
    
    --text-color-light: #776e65;
    --text-color-white: #f9f6f2;
}

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

body {
    background-color: var(--bg-color);
    color: var(--text-color-light);
    font-family: "Clear Sans", "Helvetica Neue", Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: flex-start;
    min-height: 100vh;
    padding: 24px 16px 32px;
}

.container {
    width: var(--field-width);
    max-width: 100%;
}

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

.title {
    font-size: 80px;
    font-weight: bold;
    line-height: 1;
}

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

.score-box {
    background: #bbada0;
    padding: 5px 20px;
    border-radius: 3px;
    color: white;
    text-align: center;
    min-width: 80px;
}

.score-label {
    display: block;
    font-size: 13px;
    text-transform: uppercase;
    color: #eee4da;
}

#score, #best-score {
    font-size: 25px;
    font-weight: bold;
}

#score {
    position: relative;
    display: inline-block;
}

.score-addition {
    position: absolute;
    right: -10px;
    top: -8px;
    font-size: 18px;
    font-weight: bold;
    color: #f9f6f2;
    opacity: 0;
    animation: score-up 600ms ease-out forwards;
    pointer-events: none;
}

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

#new-game-btn {
    background: #8f7a66;
    color: white;
    border: none;
    padding: 10px 20px;
    font-size: 18px;
    font-weight: bold;
    border-radius: 3px;
    cursor: pointer;
    outline: none;
}

#new-game-btn:hover {
    background: #7f6a56;
}

.game-container {
    position: relative;
    padding: var(--grid-spacing);
    background: var(--grid-color);
    border-radius: 6px;
    width: 100%;
    aspect-ratio: 1 / 1;
    height: auto;
    touch-action: none;
}

.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 {
    background: var(--empty-cell-color);
    border-radius: 3px;
    width: 100%;
    height: 100%;
}

.tile-container {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    padding: var(--grid-spacing);
    pointer-events: none;
    z-index: 10;
}

.tile {
    position: absolute;
    width: var(--cell-size);
    height: var(--cell-size);
    border-radius: 3px;
    transition: transform 130ms cubic-bezier(0.22, 0.61, 0.36, 1);
    will-change: transform;
    /* Inner content handles visual style */
}

.tile-inner {
    width: 100%;
    height: 100%;
    border-radius: 3px;
    background: #eee4da;
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: bold;
    font-size: calc(var(--cell-size) * 0.55);
    color: var(--text-color-light);
    z-index: 10;
}

/* Tile Colors - applied to inner */
.tile-2 .tile-inner { background: #eee4da; }
.tile-4 .tile-inner { background: #ede0c8; }
.tile-8 .tile-inner { background: #f2b179; color: var(--text-color-white); }
.tile-16 .tile-inner { background: #f59563; color: var(--text-color-white); }
.tile-32 .tile-inner { background: #f67c5f; color: var(--text-color-white); }
.tile-64 .tile-inner { background: #f65e3b; color: var(--text-color-white); }
.tile-128 .tile-inner { background: #edcf72; color: var(--text-color-white); font-size: calc(var(--cell-size) * 0.45); }
.tile-256 .tile-inner { background: #edcc61; color: var(--text-color-white); font-size: calc(var(--cell-size) * 0.45); }
.tile-512 .tile-inner { background: #edc850; color: var(--text-color-white); font-size: calc(var(--cell-size) * 0.45); }
.tile-1024 .tile-inner { background: #edc53f; color: var(--text-color-white); font-size: calc(var(--cell-size) * 0.35); }
.tile-2048 .tile-inner { background: #edc22e; color: var(--text-color-white); font-size: calc(var(--cell-size) * 0.35); box-shadow: 0 0 30px 10px rgba(243, 215, 116, 0.47619); }
.tile-super .tile-inner { background: #3c3a32; color: var(--text-color-white); font-size: calc(var(--cell-size) * 0.3); }

/* Animations on Inner */
.tile-new .tile-inner {
    animation: appear 200ms ease;
}

.tile-merged .tile-inner {
    z-index: 20;
    animation: pop 200ms ease;
}

@keyframes appear {
    0% { opacity: 0; transform: scale(0); }
    100% { opacity: 1; transform: scale(1); }
}

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

@keyframes fade-in {
    0% { opacity: 0; }
    100% { opacity: 1; }
}

@keyframes score-up {
    0% {
        opacity: 0;
        transform: translateY(6px);
    }
    30% {
        opacity: 1;
    }
    100% {
        opacity: 0;
        transform: translateY(-24px);
    }
}

/* Positions 1..4 */
.tile-position-1-1 { transform: translate(0px, 0px); }
.tile-position-1-2 { transform: translate(0px, calc(var(--cell-size) + var(--grid-spacing))); }
.tile-position-1-3 { transform: translate(0px, calc(2 * (var(--cell-size) + var(--grid-spacing)))); }
.tile-position-1-4 { transform: translate(0px, calc(3 * (var(--cell-size) + var(--grid-spacing)))); }

.tile-position-2-1 { transform: translate(calc(var(--cell-size) + var(--grid-spacing)), 0px); }
.tile-position-2-2 { transform: translate(calc(var(--cell-size) + var(--grid-spacing)), calc(var(--cell-size) + var(--grid-spacing))); }
.tile-position-2-3 { transform: translate(calc(var(--cell-size) + var(--grid-spacing)), calc(2 * (var(--cell-size) + var(--grid-spacing)))); }
.tile-position-2-4 { transform: translate(calc(var(--cell-size) + var(--grid-spacing)), calc(3 * (var(--cell-size) + var(--grid-spacing)))); }

.tile-position-3-1 { transform: translate(calc(2 * (var(--cell-size) + var(--grid-spacing))), 0px); }
.tile-position-3-2 { transform: translate(calc(2 * (var(--cell-size) + var(--grid-spacing))), calc(var(--cell-size) + var(--grid-spacing))); }
.tile-position-3-3 { transform: translate(calc(2 * (var(--cell-size) + var(--grid-spacing))), calc(2 * (var(--cell-size) + var(--grid-spacing)))); }
.tile-position-3-4 { transform: translate(calc(2 * (var(--cell-size) + var(--grid-spacing))), calc(3 * (var(--cell-size) + var(--grid-spacing)))); }

.tile-position-4-1 { transform: translate(calc(3 * (var(--cell-size) + var(--grid-spacing))), 0px); }
.tile-position-4-2 { transform: translate(calc(3 * (var(--cell-size) + var(--grid-spacing))), calc(var(--cell-size) + var(--grid-spacing))); }
.tile-position-4-3 { transform: translate(calc(3 * (var(--cell-size) + var(--grid-spacing))), calc(2 * (var(--cell-size) + var(--grid-spacing)))); }
.tile-position-4-4 { transform: translate(calc(3 * (var(--cell-size) + var(--grid-spacing))), calc(3 * (var(--cell-size) + var(--grid-spacing)))); }


/* Game Over / Win Message */
.game-message {
    display: none;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background: rgba(238, 228, 218, 0.73);
    z-index: 100;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    border-radius: 6px;
    animation: fade-in 800ms ease 1200ms;
    animation-fill-mode: both;
}

.game-message.game-over {
    display: flex;
}

.game-message.game-won {
    display: flex;
    background: rgba(237, 194, 46, 0.5);
    color: #f9f6f2;
}

.game-message p {
    font-size: 60px;
    font-weight: bold;
    margin-bottom: 20px;
    color: #776e65;
}

.game-message.game-won p {
    color: #f9f6f2;
}

.game-message .lower {
    display: flex;
    gap: 10px;
}

.game-message .retry-button,
.game-message .keep-playing-button {
    background: #8f7a66;
    color: #f9f6f2;
    cursor: pointer;
    border-radius: 3px;
    padding: 10px 20px;
    font-weight: bold;
    font-size: 18px;
    border: none;
    text-decoration: none;
}

.game-explanation {
    margin-top: 30px;
    font-size: 18px;
    line-height: 1.5;
}

/* Tablet */
@media screen and (max-width: 768px) {
    .title {
        font-size: 56px;
    }

    .score-box {
        padding: 5px 14px;
        min-width: 72px;
    }

    #score, #best-score {
        font-size: 22px;
    }

    .game-explanation {
        font-size: 16px;
    }
}

/* Mobile */
@media screen and (max-width: 520px) {
    :root {
        --field-width: calc(100vw - 20px);
        --grid-spacing: 10px;
    }

    body {
        padding: 12px 10px 20px;
    }

    .header {
        margin-bottom: 14px;
        align-items: flex-start;
        gap: 10px;
    }

    .title {
        font-size: 42px;
    }

    .scores-container {
        gap: 8px;
    }

    .score-box {
        padding: 4px 10px;
        min-width: 64px;
    }

    .score-label {
        font-size: 11px;
    }

    #score, #best-score {
        font-size: 20px;
    }

    .game-intro {
        flex-direction: column;
        align-items: stretch;
        gap: 10px;
        margin-bottom: 14px;
    }

    .game-intro p {
        font-size: 14px;
        line-height: 1.4;
    }

    #new-game-btn {
        width: 100%;
        font-size: 16px;
        padding: 10px 12px;
    }

    .game-message p {
        font-size: 32px;
        margin-bottom: 14px;
    }

    .game-message .retry-button,
    .game-message .keep-playing-button {
        font-size: 15px;
        padding: 9px 14px;
    }

    .game-explanation {
        margin-top: 16px;
        font-size: 14px;
        line-height: 1.45;
    }
}