Problems changing color

Hello All,
I need help.

Note: I have reduced this style question to only the problematic lines.
This is not an entire stylesheet.

When I try to change color the attached page loses functionality.

The style is simple:
div { background-color: black !important;
color: white !important;}

the site is:https://github.com/WayneEDick/NttPAdapt/upload/master/newN2tP,
but it works on any gitHub repository on the upload page.

Not this upload widget is not just GitHub. Many sites have it.

What cause this problem?

Best, Wayne