Background Video Changes Mobile Width

Is there anyway I can set a width to fix this?

Here is my site Read-Only:

Sorry, your Read-only sharing link doesn’t seem to work anymore.
Could you please re-generate it?

In case of, here’s the procedure:
1 - On your site’s dashboard click the Share icon:

2 - Generate or Copy the link:

3 - Then edit your post here and paste it inside.