@media screen and (max-width: 640px) {
    :root {   
        --margen_lateral: 10px;
    }

    header {
        grid-template-columns: 1fr 1fr;
    }

    #menu_arriba ul li {
        display: none;
    }

    #menu_arriba ul li:first-child {
        display: block;
    }

    #cabecera{
        grid-template-columns: 1fr;
    }

    #ultimospost ul{
        grid-template-columns: 1fr 1fr;
    }

    #seccion1{
        grid-template-columns: 1fr;
    }

    #seccion1 section ul{
       grid-template-columns: 1fr;
    }

    #seccionancha ul{
        grid-template-columns: 1fr;
    }

    footer{
        grid-template-columns: 1fr;
    }
}