header {
        opacity: 0;
        transition: opacity 0.3s ease;
    }
    
    header.visible {
        opacity: 1;
    }

    /* Option supplémentaire pour un effet de fade-in du haut */
    header {
        transform: translateY(-10px);
        transition: opacity 0.3s ease, transform 0.3s ease;
    }
    
    header.visible {
        opacity: 1;
        transform: translateY(0);
    }