For GoDark, it is related to youtube video 
1. Go to Admin CP > Templates and Style > Templates> GoDark> Video Embed Templates > video_youtube_embed
2. Now go to css3.css and paste it at the bottom
Now your Youtube video will be better on mobile and desktop devices.
Regards
WallBB

1. Go to Admin CP > Templates and Style > Templates> GoDark> Video Embed Templates > video_youtube_embed
Code:
<iframe class="yt_fix" src="//www.youtube.com/embed/{$id}" frameborder="0" allowfullscreen></iframe>
2. Now go to css3.css and paste it at the bottom
Code:
@media only screen and (min-width: 769px) {
.yt_fix {
width: 560px;
height: 315px;
}
}
Regards
WallBB