Here is a small snippet to modify the background of yours videos.

Just like this: Hover me

Just add the following css in the “advanced customization” section of your editor:

.video-view .sprite {
background-size: 15%;
background-position: 96% 80%;
}

To change the size of your player, you can modify the percentage value of “background-size” with your own value.
And to change the position, you can modify the percentage value of “background-position“.

Information:
The first percentage of “background-position” is the left gap, the second is the top gap.