.container {
    display: grid;
    grid-template:
        "header header header"
        "sidebar main sidebar"
        "footer footer footer"
            /1fr 2fr 1fr;
    gap: 10px 10px;
}

header { grid-area: header; }
aside { grid-area: sidebar; }
main { grid-area: main; }
footer { grid-area: footer; }