I want to make the overall desktop look a bit more consistent!
How to do that?
For example, in this image, as you can see the Brave Browser has the traditional windows looking cross button, but Mozilla firefox has the system red coloured cross.
In Brave, under Settings, is an option for "Use System Title bar and borders" (or similar), with a slide switch for activation. I suspect that might help...
For "whole system" - the answer may be more involved, depending on what else gives trouble!