As you can see on attached images, this addon will turn all your default UI black. Nothing else. Addon is extremly lightweight.
Even though addon is called 'UI', in fact it is just a usual addon you can install and enable as any other addon. No need to copy WTF folder or whatever. Just plug&play.
You can right-click on minimap to open calendar and middle-click to open 'find'.
Many thanks to Zork and Wildbreath for their ideas, you guys are awesome.
1.0.1. Alternate mana/power bar and combopoints are now styled.