body {
            margin: 0;
            overflow: hidden;
            background: #0f1117;
            color: #e2e8f0;
            font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
            user-select: none;
        }
        #game-container {
            position: relative;
            width: 100vw;
            height: 100vh;
        }
        canvas {
            display: block;
        }
        #ui-layer {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            pointer-events: none;
        }
        .hud {
            position: absolute;
            padding: 20px;
            pointer-events: auto;
        }
        #xp-bar-container {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 10px;
            background: rgba(255,255,255,0.1);
        }
        #xp-bar {
            width: 0%;
            height: 100%;
            background: linear-gradient(90deg, #00f2fe 0%, #4facfe 100%);
            box-shadow: 0 0 10px #4facfe;
            transition: width 0.3s;
        }
        .stats {
            top: 20px;
            left: 20px;
            font-size: 24px;
            font-weight: bold;
            text-shadow: 2px 2px 4px #000;
        }
        #overlay {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            background: rgba(15, 17, 23, 0.9);
            padding: 40px;
            border-radius: 20px;
            border: 2px solid #4facfe;
            text-align: center;
            pointer-events: auto;
            display: block;
        }
        .btn {
            background: #4facfe;
            color: white;
            border: none;
            padding: 15px 40px;
            font-size: 20px;
            border-radius: 30px;
            cursor: pointer;
            margin-top: 20px;
            transition: transform 0.2s, background 0.2s;
        }
        .btn:hover {
            transform: scale(1.05);
            background: #00f2fe;
        }
        #upgrade-menu {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            display: none;
            gap: 20px;
            pointer-events: auto;
        }
        .upgrade-card {
            background: #1a1c23;
            border: 1px solid #4facfe;
            padding: 20px;
            width: 200px;
            border-radius: 10px;
            cursor: pointer;
            transition: 0.2s;
        }
        .upgrade-card:hover {
            background: #2a2c33;
            transform: translateY(-10px);
        }