Better contract between active and inactive windows

### Problem

Currently it's not possible to see which window is active and which one is inactive, apart from checking the shadow and which app is in the foreground:

When there is disconnect between keyboard input and the active window, it's not clear where shortcuts are actioning or where keyboard input is entered, especially as some background inputs can still show a cursor.

### Proposal

The titlebar icons and shadow do change slightly but I think elementaryOS would benefit from having the foreground window be more prominent in some way.

### Prior Art (Optional)

_No response_