.rt-video {
    margin-top: 16px;
    position: relative;
    width: 100%;
    max-width: 900px;
    padding-bottom: 498px;
}
.rt-video iframe {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
}

@media(max-width: 900px) {
    .rt-video {
        padding-bottom: 56%;
    }
}