If you want to improve the look & feel of the code in your xojo.com IDE you might want to give JetBrains Mono Font a try. You can download it for free here.

After having installed the font on your system, you can use it in your IDE by changing the system font in the preferences of the XOJO IDE.

Your code will now show the newly installed JetBrains Mono font, which is far better readable and monospaced.