*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

 
body{
    background-color: #20201e;
    color: #fff;
    font-family: 'Montserrat', sans-serif;
}


.parent{
    display: grid;
    grid-template: 90px 450px 90px / repeat(12, 1fr);
    grid-gap: 1em;

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

.header{
    background-color: #646435;
    padding: 1em;
    grid-area: h;
}

.menu{
    background-color: #e43b3b;
    padding: 1em;
    grid-area: m;
}

.content{
    background-color: #8ee75e;
    padding: 1em;
    grid-area: c;

}

.footer{
    grid-area: f;
    background-color: #6b95e9;
    padding: 1em;
}

div:nth-child(4){
        propiedad: valor;
    }