#main {
    display: flex;
    min-height: calc(100vh - 20vh);
}
#main > article {
    flex: 1;
}
#main > nav,
#main > aside {
    flex: 0 0 20vw;
    background: #ffffff;
}
#main > nav {
    order: -1;
}

header {
    display:flex;
    justify-content: center;
    align-items: center;
    font-size: 140%;
}

.iframe-container {
    overflow: hidden;
    /* 16:9 aspect ratio */
    padding-top: 56.25%;
    position: relative;
}
.iframe-container iframe {
    border: 0;
    height: 100%;
    left: 0;
    position: absolute;
    top: 0;
    width: 100%;
}