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

.contenedor{
    padding: 10px;
    background: lightgreen;
    display: grid;
    height: 100vb;
    grid-template-columns: 20% auto 20%;
    grid-template-rows: 20% auto 17%;
    grid-template-areas: "n h a"
                         "n m a"
                         "n f f";
}

header{
    grid-area: h;
}

nav{
    grid-area: n;
}

main{
    grid-area: m;
}

aside{
    grid-area: a;
}

footer{
    grid-area: f;
}

.elemento{
    background: lightblue;
    border: 3px solid blue;
    font-size: 2rem;
    text-align: center;
}