Changes to AJAX translation pages
Fragment of a discussion from Translation UX feedback
Monobook was re-enabled several months ago.
To determine whether what you are seeing is MediaWiki UI, you can compare to the screenshot I linked (the inspect tool of your browser may also help): generally it's distinguished by the fatness of objects, abundance of whitespace and mild/pastel colours.
Which screenshot? Your answer is very cryptic to me.
I do have a little personal .css but the only color related statement there is:
.diffchange-inline { color:black }
which cannot be responsible for blue texts on blue backgrounds.
I tried Monobook and got the same blue-on-blue-mess and the same half-heigt-background-colour-split lines as before.