Customize Apache Nifi Frontend

I want to implement Apache Nifi on my webapp and i need to customize a little bit the UI to make it more compliant with my app. I have some troubles in understanding where is the code of frontend in the Source2.0.0-M2 package you can download from the official website.

Where can I find the code? Thank you in advance.

I have tried to change the js code in multiple folders but nothing has changed.