Classic theme looks the same as the default theme in 4.40.0.20260604-0652 on Linux

Let's make sure issue is not already fixed in latest builds first.

- [ ] I verified I can reproduce this issue against [latest Integration Build of Eclipse SDK](https://download.eclipse.org/eclipse/downloads/)

## Steps to reproduce

From a fresh installation and clean workspace:

Light & Default

Looks the same as Light & Classic (changed the pref and restarted Eclipse):

I expected: Classic to have round corner on tab headers and a bit more contrastive colors.

But got: Classic looking the same as Default

## Here is some relevant log output

Not sure what to look for in `/.metadata/.log`. Please advise.

## Tested under this environment:
* OS & version: KDE Plasma@Linux
* Eclipse IDE/Platform version (as shown in *Help > About*): 4.40.0.20260604-0652

## Community

- [x] I understand reporting an issue to this OSS project does not mandate anyone to fix it. Other contributors may consider the issue, or not, at their own convenience. The most efficient way to get it fixed is that I fix it myself and contribute it back as a good quality patch to the project.