.djangocms-video-plugin {
    position: relative;
    /* this is the height of a 16:9 box */
    padding-bottom: calc(100% / (16/9));
    padding-top: 30px;
    height: 0;
    overflow: hidden;
}

.djangocms-video-plugin iframe, object, embed, video {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}