Wow, you unlocked a memory. In case somebody doesn't remember, or doesn't know, the style of Borland buttons, here's a screenshot: https://sourceforge.net/p/owlnext/wiki/Replacing_usage_of_BW...
Some more screenshots on this page: https://www.drbob42.com/delphi/findmapc.htm
(Look at all those misaligned icons/labels in the Tool Options screenshot!)
- Office (custom widget toolkit, menus, toolbars, etc)
- Internet Explorer (frequently introduced new toolbar designs not available to apps via API until later)
- Encarta (custom dark mode-ish theme)
- Netscape Communicator (custom toolbars)
- RealPlayer
- QuickTime
- MSN Messenger (custom theme)
- Every video game ever
... UI inconsistency didn't arrive with the web. Even macOS has always been a patchwork. Apple couldn't stop introducing new themes over time and there were always apps that didn't quite follow. Brushed metal!
Now, if I take a couple of current applications, the differences are much bigger: from the top of my head, Explorer, Settings, Edge, Office, Steam, Spotify all have much more unique UIs.
Then XP kind of broke that as so many started not bothering and then it all went sideways.