osTicket plugin that allows for inserting custom CSS and JS code to the client and staff interfaces.
Disclaimer: This is not the ideal solution, but works well and is upgrade-proof without amending core files.
You will need to convert to phar before uploading to /include/plugins directory.
Good tool to use: https://phar.scer.io/
Just Zip the files up, and drag the zip file into the window.
Feel free to contribute improvements...