You can look at the source code yourself -- this one relies on a couple CSS files and Javascript.

Here's where you'd find the ability to inspect at least within Brave browser, under the main menu. Then just click whichever file you're looking to read the source for first. Usually best to start with (Index) as everything else is getting called from it.

That said, I know most people don't do web coding by hand nearly as much as we used to (and the web is grosser for it). Can't say I know what sort of tools got used to generate this. But hope it gives you some understanding of what's going on!