Maybe this needs a new thread, I dunno.
I've managed to make a few changes in the dark theme .xml file. I had to copy the file to the desktop, make the changes there, then copy back to the syntax folder. It's laborious but it works.
This theme looks like an unfinished project. Partly because there's a 'fix me' comment embedded. Partly because some of the color combinations don't work. One thing I changed was the colors used to highlight matching brackets, etc.
A related issue: If you cursor on to say, a closing curly brace and the opening mate for that is off-screen at the top a box is shown presenting the code of the matching off-screen line. The non-keyword text that appears there is invisible.
Question - what is the term for the message box? If I knew what to look for I could tinker with the colors but, most of that file is a mystery.
I tried to make the image bigger but couldn't.