How to change default admin theme?

The default admin colors on pages such as ‘edit post’, of white on very pale blue with a slightly less pale blue frame are very difficult for me to distinguish.

I’ve looked through dozens of ‘admin themes’, and can’t find anything that lets me change this color scheme. I’ve looked at the css, but between all of the nested classes, I can’t figure out what to change where. (I know, the changes need to go into a child theme of some sort, but I can’t even figure out what/where that would be/go.)

Any suggestions.