Video backgrounds
Backgrounds are ready-made video loops. There's no prompt — you download the file or copy its link, then embed it. It's the one category where an AI has nothing to generate.
You can't prompt your way to a video. A background isn't code to recreate, it's an asset to use: grab the file, or a link to it, and put it in your page.
A background should sit behind your content without competing with it — in practice, lower contrast and slower motion than feels right when you view it on its own.
When to use it
When a hero or section needs motion and depth, and a 3D scene would be more weight than the moment calls for.