* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
body {
    width: 100vw;
    height: 100vh;
    background-color: silver;

    display:grid;
    grid-template-columns: 1fr;
    grid-template-rows: auto 1fr;
}
main {
    overflow: hidden;
}
header {
    min-height: 50px;
    background-color: honeydew;
}

main .content {
    width: 100%;
    height: 100%;
}