.container {
    grid-template-areas: 
        "h h h h h h h h h h h h h h"
        ". m m m m c c c c c c c c ."
        "f f f f f f f f f f f f f f";
}

@media screen and (max-width: 640px) {  

    .container {  

    grid-template-areas: 
        "h h h h h h h h h h h h h h"
        "m m m m c c c c c c c c c c"
        "f f f f f f f f f f f f f f";
    }   
}