You are viewing the page with OasisRevived, so it's more a problem with that script than with the wiki's logo. In normal view, there is no background color to the header.

There is a background on the scrolling header, and it looks pretty much like that.

Ah I see now - the problem is on dark mode, the contrast in light mode is totally fine in my opinion.

Yeah, it is the dark mode. With OasisRevived.