body {
            margin: 0;
            padding: 0;
            height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            background-image: url("images/Bg.gif"); /* Remplace par ton image */
            background-size: cover;
            background-position: center;
            font-family: Arial, sans-serif;
        }

        #contenu {
            text-align: center;
            color: white;
            opacity: 0;
            transition: opacity 2s ease-in-out;
        }

        #contenu h1 {
            font-size: 2.5em;
            text-transform: uppercase;
            margin-bottom: 20px;
            background: rgba(0,0,0,0.5);
            padding: 15px;
            border-radius: 10px;
        }

        /* Bouton animé avec dégradé vert */
        #startBtn {
            padding: 15px 30px;
            font-size: 1.2em;
            color: white;
            border: none;
            border-radius: 8px;
            cursor: pointer;
            background: linear-gradient(270deg, #00ff88, #009944);
            background-size: 400% 400%;
            animation: gradientMove 3s ease infinite;
        }

        @keyframes gradientMove {
            0% { background-position: 0% 50%; }
            50% { background-position: 100% 50%; }
            100% { background-position: 0% 50%; }
        }