More CSS variable support

[FelixBlaisThon]

We are using Mantine as the source of our react component for our app (which we enjoy quite a lot!), but we were wondering if it would be possible to add some CSS variable for components so that we can leverage the customization to the next level. I know we could go headless, but we want to find a sweet spot between having to style the whole universe and style just enough for our need (and maybe others). Let's say the button for example, I would add a new variable like

'--button-disabled-bg'
'--button-disabled-color'

We plan to add more, for more components, but we wanted to touch base first to see if it was something possible.

Thank you!