Previously, the titlebar had its own color, but now, with Breeze light, the titlebar blends with the window content. However, some programs still have separators such Dolphin settings and System Settings. There are more programs with this problem, though.

Maybe removing those lines or making them gradient would help. Also, some parts of the system like Dolphin settings content have an outline that change is color indicating that is focused. That might not be necessary since the items in the left panel, such as general, startup, etc, already get selected when clicking on them.

Possible solution:
These separators could have a gradient, to make a smooth transition.