How to remove black rectangles around video container?

I have 1:1 format videos on my site. The video containers are more like 2:1 with black rectangles around the video thumbnails. I want them to be removed, but don’t know how. Please give me advice how to make the video containers either 1:1 rectangle or how to change the black background color to white, thank you.

You can see here what I mean: https://www.balanse.fi/tauko-balanse/

There do not appear to be videos on that page.