:root {
    --board-size: min(400px, calc(100vw - 70px));
    --board-gap: 10px;
    --animation-duration: 80ms;
}

* {
    box-sizing: border-box;
}

body {
    min-height: 100vh;
    min-height: 100dvh;
    margin: 0;
    padding: max(20px, env(safe-area-inset-top)) max(20px, env(safe-area-inset-right)) max(20px, env(safe-area-inset-bottom)) max(20px, env(safe-area-inset-left));
    overflow-x: hidden;
    overflow-y: auto;
    background: #faf8ef;
    color: #776e65;
    font-family: "Clear Sans", "Helvetica Neue", Arial, sans-serif;
    -webkit-tap-highlight-color: transparent;
}

#game-shell {
    display: flex;
    min-height: calc(100vh - 40px);
    min-height: calc(100dvh - 40px);
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

#game-container {
    position: relative;
    margin-bottom: 20px;
    padding: 15px;
    border-radius: 6px;
    background: #bbada0;
    box-shadow: 0 0 15px rgb(0 0 0 / 20%);
    touch-action: none;
    user-select: none;
}

.header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 10px;
}

h1 {
    margin: 0;
    color: #776e65;
    font-size: 3.5em;
    font-weight: 700;
    line-height: 1;
}

.score-container {
    position: relative;
    min-width: 80px;
    padding: 8px 15px;
    overflow: hidden;
    border-radius: 3px;
    background: #eee4da;
    font-size: 1.2em;
    font-weight: 700;
    text-align: center;
}

.score-title {
    margin-bottom: 2px;
    color: #6a6a6a;
    font-size: 0.8em;
}

.score-animation {
    position: absolute;
    top: 50%;
    left: 50%;
    color: #8f7a66;
    font-weight: 700;
    animation: score-pop 0.5s ease-out forwards;
}

@keyframes score-pop {
    from { transform: translate(-50%, 0); opacity: 1; }
    to { transform: translate(-50%, -100%); opacity: 0; }
}

#game-board {
    position: relative;
    display: grid;
    width: var(--board-size);
    aspect-ratio: 1;
    grid-template: repeat(4, 1fr) / repeat(4, 1fr);
    gap: var(--board-gap);
    overflow: hidden;
}

.cell {
    width: 100%;
    height: 100%;
    border-radius: 3px;
    background: rgb(238 228 218 / 35%);
}

.tile {
    position: absolute;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 3px;
    font-weight: 700;
    transition: left var(--animation-duration) ease-out, top var(--animation-duration) ease-out, transform var(--animation-duration) ease-out, opacity var(--animation-duration) ease-out;
    will-change: left, top, transform;
}

.tile.new-tile { animation: pop-in 0.15s ease-out; }
.tile.merged-tile { animation: merged-pop 0.15s ease-in-out; }

@keyframes pop-in {
    0% { transform: scale(0); opacity: 0; }
    50% { transform: scale(1.1); opacity: 1; }
    100% { transform: scale(1); opacity: 1; }
}

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

.tile-2 { background: #eee4da; color: #776e65; font-size: 2.5em; }
.tile-4 { background: #ede0c8; color: #776e65; font-size: 2.5em; }
.tile-8 { background: #f2b179; color: #f9f6f2; font-size: 2.2em; }
.tile-16 { background: #f59563; color: #f9f6f2; font-size: 2.2em; }
.tile-32 { background: #f67c5f; color: #f9f6f2; font-size: 2.2em; }
.tile-64 { background: #f65e3b; color: #f9f6f2; font-size: 2.2em; }
.tile-128 { background: #edcf72; color: #f9f6f2; font-size: 2em; }
.tile-256 { background: #edcc61; color: #f9f9e8; font-size: 2em; }
.tile-512 { background: #edc850; color: #f9f9e8; font-size: 2em; }
.tile-1024 { background: #edc53f; color: #f9f9e8; font-size: 1.8em; }
.tile-2048 { background: #edc22e; color: #f9f9e8; font-size: 1.8em; }
.tile-4096 { background: #3c3a32; color: #f9f9e8; font-size: 1.8em; }
.tile-8192 { background: #007bff; color: #f9f9e8; font-size: 1.7em; }
.tile-16384 { background: #6f42c1; color: #f9f9e8; font-size: 1.6em; }
.tile-32768 { background: #28a745; color: #f9f9e8; font-size: 1.5em; }
.tile-65536 { background: #dc3545; color: #f9f9e8; font-size: 1.4em; }
.tile-higher { background: #000; color: #f9f9e8; font-size: 1.3em; }

#game-over-screen {
    position: absolute;
    z-index: 10;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    border-radius: 6px;
    background: rgb(255 255 255 / 70%);
    color: #776e65;
    font-size: 2em;
    font-weight: 700;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s ease-in-out;
}

#game-over-screen.visible { opacity: 1; pointer-events: auto; }

.button-row {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 10px;
}

.new-game-button {
    min-height: 44px;
    padding: 10px 20px;
    border: 0;
    border-radius: 3px;
    background: #8f7a66;
    color: #f9f6f2;
    cursor: pointer;
    font-size: 1em;
    font-weight: 700;
    touch-action: manipulation;
}

.new-game-button:hover { background: #9f8b78; }
.auto-play-button { background: #5cb85c; }
.auto-play-button:hover { background: #4cae4c; }
.auto-play-button.active { background: #d9534f; }
.auto-play-button.active:hover { background: #c9302c; }

@media (max-width: 500px) {
    :root { --board-size: min(320px, calc(100vw - 40px)); --board-gap: 8px; }
    body { padding: 10px; }
    #game-shell { min-height: calc(100dvh - 20px); }
    #game-container { padding: 10px; }
    h1 { font-size: 2.5em; }
    .score-container { min-width: 60px; padding: 6px 10px; font-size: 1em; }
    .tile-2, .tile-4 { font-size: 2em; }
    .tile-8, .tile-16, .tile-32, .tile-64 { font-size: 1.8em; }
    .tile-128, .tile-256, .tile-512 { font-size: 1.6em; }
    .tile-1024, .tile-2048, .tile-4096 { font-size: 1.4em; }
    .tile-8192, .tile-16384 { font-size: 1.2em; }
    .tile-higher { font-size: 0.9em; }
}

@media (max-height: 560px), (orientation: landscape) and (max-height: 500px) {
    #game-shell { min-height: 0; justify-content: flex-start; }
    :root { --board-size: min(280px, calc(100vw - 40px), calc(100dvh - 105px)); --board-gap: 6px; }
    #game-container { margin-bottom: 10px; }
    h1 { font-size: 2em; }
}

@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        scroll-behavior: auto !important;
        animation-duration: 1ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 1ms !important;
    }
}