Change default render of UI nodes?

This maybe a loaded question, no pun intended, but I would like to have the default scheme for dashboard UI controls to not be white text on teal background, but to say black text on red background? Yes I can configure and send msg parts to change the color/background color, but this is at times slow, on complex panels that you see of default colors flicker before the initial message occurs. Would maybe a CSS file allow such? I am talking about doing this across entire tabs, and groups on tabs, etc.

If I change the 'widget' colors under a custom theme is that going to be consistent across the default set of UI controls?

I might be wrong in understanding your question, but isn't this what this is supposed to achieve?

My initial question yes, the follow up, was if the UI controls all honor the theme, which given the quick check I did, for what I typically use, it does.