App does not play well with OSX Dark theme

[lpbas]

Hello. I would like to thank you for this amazing converter, it has saved me so much time lately. Today I was trying the OSX Dark Theme and I found out that the colours of the code in both Swift and Kotlin windows are not readable, since the normal code is coloured black, and the background is dark grey.

This should either be changed to white when the dark theme is enabled, or a "dark text editor" colour scheme should be added.

I'll try to take a shot at this when I find some time, I suppose it should not be very hard.