To make a Popup like that one and it’ll close when you click on the x

For what purpose? If you're trying to use one for your userpage, that is likely not allowed.

Uh why is it not allowed? They aren’t allowing popups now?

See Talk:Banner.

So that’s a banner and it’s not allowed on wikis anymore?

If you are looking for a Wikitext version of this type of boxes, I have made one on https://lost-cities-keeper.fandom.com/wiki/Template:FloatingBox

The talk page KockaAdmiralac linked seems to be restricting sitewide notices, I may be wrong but I don't think it really refers to any fixed-position element.

Cool, thanks!

How do i do this idc the tos

@Thenewlayoutblowsthrowscomputerintoilet Unwise.

Well, Fandom did approve the update to BannerNotification. I guess I am not clear on what the significant difference between the two is. It looks to me like they are using the same system.