Hmm, it's okay, but just leaves some blank space on the right.

I tried to fix it, adding these to yours seems to work okay:

    youtube.com###related:upward(#secondary)
    youtube.com##:root:not(:fullscreen) video:matches-css(left: 0px):style(object-fit: fill!important; width: 100%!important; height: auto!important;)