*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{--bg:#faf8ef;--text:#776e65;--header-bg:#faf8ef;--header-border:#e0d8c8;--grid-bg:#bbada0;--cell-bg:#cdc1b4;--accent:#8f7a66;--modal-bg:#fff;--modal-text:#776e65;--overlay-bg:rgba(238,228,218,0.73)}
[data-theme="dark"]{--bg:#1a1a2e;--text:#e0e0e0;--header-bg:#16213e;--header-border:#0f3460;--grid-bg:#3a3a5c;--cell-bg:#4a4a6a;--accent:#6c8cbf;--modal-bg:#16213e;--modal-text:#e0e0e0;--overlay-bg:rgba(0,0,0,0.6)}
html,body{height:100%;font-family:'Inter',sans-serif;background:var(--bg);color:var(--text);-webkit-user-select:none;user-select:none}
body{display:flex;justify-content:center}
.app{width:100%;max-width:500px;display:flex;flex-direction:column;align-items:center}
.app-header{width:100%;display:flex;align-items:center;justify-content:space-between;padding:12px 16px;background:var(--header-bg);border-bottom:1px solid var(--header-border)}
.app-title{font-size:1.5rem;font-weight:800;color:var(--text)}
.icon-btn{background:none;border:none;cursor:pointer;color:var(--text);padding:6px;border-radius:8px;display:flex;align-items:center;justify-content:center;width:36px;height:36px}
.icon-btn:hover{background:rgba(128,128,128,0.15)}
.icon-btn svg{width:20px;height:20px}
[data-theme="light"] .icon-moon{display:none}[data-theme="dark"] .icon-sun{display:none}[data-theme="dark"] .icon-moon{display:block}
.game-container{padding:16px;display:flex;flex-direction:column;align-items:center;gap:12px;width:100%}
.score-bar{display:flex;gap:10px}
.score-box{background:var(--grid-bg);color:#fff;border-radius:8px;padding:8px 20px;text-align:center;min-width:80px}
.score-label{font-size:.65rem;font-weight:600;text-transform:uppercase;opacity:.7}
.score-value{font-size:1.3rem;font-weight:700}
.grid{position:relative;background:var(--grid-bg);border-radius:8px;padding:8px;width:min(calc(100vw - 32px),340px);aspect-ratio:1}
.grid-bg{position:absolute;inset:8px;display:grid;grid-template:repeat(4,1fr)/repeat(4,1fr);gap:8px}
.grid-bg::before,.grid-bg::after{content:'';display:none}
.cell-bg{background:var(--cell-bg);border-radius:6px}
.tiles{position:absolute;inset:8px}
.tile{position:absolute;display:flex;align-items:center;justify-content:center;font-weight:700;border-radius:6px;transition:top 150ms ease-in-out,left 150ms ease-in-out;will-change:top,left}
.tile-new{animation:appear 120ms ease backwards}
.tile-merged{animation:pop 150ms ease}
@keyframes appear{from{transform:scale(0);opacity:0}to{transform:scale(1);opacity:1}}
@keyframes pop{0%{transform:scale(1)}50%{transform:scale(1.2)}100%{transform:scale(1)}}
.new-game-btn{padding:10px 28px;font-family:inherit;font-size:.9rem;font-weight:600;border:none;border-radius:8px;background:var(--accent);color:#fff;cursor:pointer}
.new-game-btn:hover{opacity:.9}
.hint{font-size:.75rem;opacity:.5}
.modal-overlay{position:fixed;inset:0;background:var(--overlay-bg);display:none;align-items:center;justify-content:center;z-index:100}
.modal-overlay.active{display:flex}
.modal{background:var(--modal-bg);color:var(--modal-text);border-radius:16px;padding:32px 28px;text-align:center;max-width:320px;width:90%;box-shadow:0 12px 40px rgba(0,0,0,0.2)}
.modal-title{font-size:1.25rem;font-weight:700;margin-bottom:4px}
.modal-sub{font-size:.85rem;opacity:.7;margin-bottom:12px}
.win-icon{font-size:48px;margin-bottom:8px}
.final-score{font-size:1.2rem;font-weight:700;margin-bottom:16px}
.play-again-btn{width:100%;padding:12px;font-family:inherit;font-size:1rem;font-weight:600;border:none;border-radius:10px;background:var(--accent);color:#fff;cursor:pointer;margin-bottom:8px}
.secondary-btn{width:100%;padding:10px;font-family:inherit;font-size:.85rem;font-weight:600;border:1px solid var(--accent);border-radius:10px;background:transparent;color:var(--accent);cursor:pointer}