Sadly, I'm no longer maintaining this theme. The Arduino IDE has changed a lot but I'm not doing much work with the platform and it's just too much to keep this up-to-date. If you'd like to fork the repo and fix it, that would be great! I'll happily add a link to your version here so others can benefit.

Still works for Arduino version 1.8.5+, not tested with newer/older versions.

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• Mac users should look in /Applications/Arduino.app/Contents/Java/lib and replace the theme folder inside (making a copy of the original in case want to revert back).
• Windows is located in C:\Program Files (x86)\Arduino\lib.
• Linux will be in /usr/share/arduino/lib/ – note you may need to install the Arduino IDE from the Arduino site, not a place like Ubuntu Software

The newest version of the Arduino IDE makes creating custom themes trickier: you now need to edit the theme.txt file, an XML file inside the syntax folder, and the button files. Unfortunately, not all items in the theme.txt file actually work, so if you can't get an item to change, try another one of the files.

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Released under Creative Commons BY-NC-SA license - feel free to use but please let me know.