:root {
                --primary: #4caf50;
                --bg: #f5f7fa;
                --card-front: #ffffff;
                --card-back: #ccc;
                --card-match: #81c784;
                --text-dark: #2e2e2e;
                --shadow: rgba(0, 0, 0, 0.1);
                --highlight: #e8f5e9;
                --alert-bg: #fff3cd;
                --alert-border: #ffeeba;
                --alert-text: #856404;
            }

            * {
                box-sizing: border-box;
                user-select: none;
                -webkit-user-select: none;
                font-family: "Segoe UI", sans-serif;
            }

            body {
                background: var(--bg);
                margin: 0;
                padding: 0.6rem;
                color: var(--text-dark);
                display: flex;
                flex-direction: column;
                align-items: center;
                overflow-x: hidden;
                -webkit-touch-callout: none;
                -webkit-user-select: none;
                -khtml-user-select: none;
                -moz-user-select: none;
                -ms-user-select: none;
                user-select: none;
                -webkit-user-drag: none;
                -webkit-tap-highlight-color: transparent;
            }

            h1 {
                font-size: 2rem;
                margin-bottom: 0.5rem;
                margin-top: 0rem;
            }

            #level,
            #timer {
                display: inline-block;
                font-size: 1.2rem;
                font-weight: bold;
                background: var(--highlight);
                border: 2px solid var(--primary);
                border-radius: 8px;
                padding: 0.5rem 1rem;
                margin: 0.4rem;
                box-shadow: 0 2px 4px var(--shadow);
            }

            .info-container {
                display: flex;
                gap: 1rem;
                margin-top: 0.5rem;
                flex-wrap: wrap;
                justify-content: center;
            }

            .board {
                display: grid;
                grid-template-columns: repeat(auto-fit, minmax(50px, 1fr));
                gap: 0.75rem;
                max-width: 350px;
                margin-top: 1.2rem;
                width: 100%;
            }

            .card {
                width: 100%;
                padding-top: 100%;
                position: relative;
                background: var(--card-back);
                border-radius: 10px;
                box-shadow: 0 2px 6px var(--shadow);
                cursor: pointer;
                transition: transform 0.2s ease;
            }

            .card.open {
                background: var(--card-front);
                transform: scale(1.05);
            }

            .card.matched {
                background: var(--card-match);
                color: white;
                cursor: default;
            }

            .card span {
                position: absolute;
                top: 50%;
                left: 50%;
                transform: translate(-50%, -50%);
                font-size: clamp(1.5rem, 5vw, 2rem);
            }

            .btn {
                margin-top: 1.5rem;
                padding: 0.75rem 1.5rem;
                font-size: 1rem;
                background: var(--primary);
                color: white;
                border: none;
                border-radius: 8px;
                cursor: pointer;
                box-shadow: 0 2px 4px var(--shadow);
            }

            .btn + .btn {
                margin-left: 0.5rem;
            }

            #game-over,
            #start-screen {
                margin-top: 2rem;
                text-align: center;
            }

            #game-over {
                background-color: var(--alert-bg);
                border: 1px solid var(--alert-border);
                border-radius: 10px;
                padding: 1.5rem;
                box-shadow: 0 2px 6px var(--shadow);
                max-width: 300px;
            }

            #game-over p {
                font-size: 1.2rem;
                color: var(--alert-text);
                margin-bottom: 1.2rem;
            }

            .confetti {
                position: fixed;
                top: 0;
                left: 0;
                width: 100%;
                height: 100%;
                pointer-events: none;
                overflow: hidden;
                z-index: 9999;
            }

            .confetti span {
                position: absolute;
                font-size: 1.5rem;
                animation: fall 2s linear infinite;
            }

            @keyframes fall {
                0% {
                    transform: translateY(-100%) rotate(0deg);
                    opacity: 1;
                }
                100% {
                    transform: translateY(100vh) rotate(360deg);
                    opacity: 0;
                }
            }