Let's get those videos covered

Static object-fit video background

We're using object-fit to have the video always cover its container

Vimeo hosted CMS video background

This is where the magic happens. Inserting the Vimeo Pro ID in the embed element together with object-fit we get the wanted responsive behavior in CMS items. They're greyed out here as I currently down own a Vimeo Pro plan myself.

Webflow hosted CMS video background

If you want both MP4 and Webm like Webflow delivers through the standard video background element, you can set it up like this collection

Webflow standard video background

Nothing exciting to see here. This is the standard background video element. But sadly it doesn't work for CMS items. Upload your video here, inspect the element in Chrome and snap the source links to put into your collection.