.video_bg_section > * { position: relative; z-index: 10; }
.video_bg_section > .video_bg_wrapper{
    position: absolute;
    left: 0; top: 0; bottom: 0; right: 0; z-index: 0;
}
.video_bg_section > .video_bg_wrapper .video_bg{
    width: 100%; height: 100%; position: relative;
}

.video_bg > picture {
    position: absolute;
    top: 0; left: 0; bottom: 0; right: 0;
    width: 100%; height: 100%;
}
.video_bg > video {
    opacity: 0;
    transition: all 1s ease;
}
.video_bg.video_loaded > video {
    opacity: 1;
}