:root {
    --WindowFull : 100svh;
    --TopHeight: 50px;
    --FooterHeight: 120px;
}

body, html {
    background-color: black;
    margin: 0px;
    margin-left: 2.5%;
    margin-right: 2.5%;
    height: 100lvh;
    width: 95%;
}

header {
    align-content: center;
    position: relative;
    background-color: Gray;
    height: var(--TopHeight);
}

#content {
    position: relative;
    height: calc(var(--WindowFull) - calc(var(--FooterHeight) + var(--TopHeight)));
}

#content > * {
    margin-top: 5px;
    margin-bottom: 5px;
}

footer {
    align-content: center;
    position: relative;
    height: var(--FooterHeight);
    background-color: aquamarine;
}