:root {
    --bg-color: #aaa;
    --text-color: black;
    --other-background: #444;
}

body {
    margin: 0;
    width: auto;
    height: auto;
    background-color: var(--bg-color);
}

header {
    background-color: var(--other-background);
    height: 50px;
}
.content {
    width: 100%;
    height: calc(100% - 55px);
    margin: initial;
}

.flex {
    display: flex;
    flex-direction: column;
}

.flex>* {
    flex-flow: column;
    /* width: 1fr;
    height: 1fr; */
    /* background-color: aquamarine; */
    margin: auto;
}

footer {
    position: fixed;
    bottom: 0;
    width: 100%;
    height: 40px;
    background: var(--other-background);
}
footer.flex {
    flex-direction: row;
}