body {
    display: grid;
    height: 100vh;
    grid-template: auto 1fr auto / 300px 1fr auto;
    font-weight: bold;
}

header {
    background: lightpink;
    padding: 2rem;
    grid-column: 1 / 4;
}

main {
    background: coral;
    grid-column: 1/3;
}

.right-sidebar {
    background: yellow;
    grid-column: 3 / 4;
}

footer {
    background: wheat;
    padding: 2rem;
    text-align: center;
    grid-column: 1 / 4;
}

.main,
.right-sidebar {
    padding: 1rem;
}