There are multiple additions to the “Themes” tool that I think would be worthwhile.
1) The ability to change fonts for both the code and the output on the console.
Personally I have tried to develop a theme that resembles the Thonny IDE for its accessibility, being able to change the font and font size would also help with readability.
2) The ability for the code syntax theme to allow for keywords etc to be in bold or italic.
This allows for more contrast between different tag types. Some IDEs have this set by default, and therefore it may feel more natural for some.
3) Change the width of outlines.
I also find that the default width of outlines in Replit is way too thin, if you use colours that are similar to each other it is almost impossible to see. Being able to change the width would help solve this.
4) Be able to add your own categories to the code syntax theme by typing in a keyword.
Again when trying to get a theme that resembles the light theme from Thonny, i found there was no way to separately make tags things like parameter tags of classes a lighter shade of purple.
5) Split up the ‘primary’ theme between text, buttons and etc.
I personally find this to be an incredibly irritating feature. It means that its difficult to get any contrast between the text and button colour on the left hand menu when using the IDE. It means that you have to try and find a colour that makes text visible in the file text and left hand menu, as well as making the cursor visible and find a balance between the text and button colour on the left hand menu, which is difficult.
There are a few other small features that would also be useful, like being able to add a background colour for open strings and brackets, pre-set layouts, or change the background boxes for the files, console and buttons from rounded squares to regular squares.