I can't edit the main page of the Habpanel

Hi everyone!
I hope you are doing well.
I need your help because I’m beginner in this part.
I’m going to edit the main page of the habpanel, but I can’t find the html, css, js files.
I think I have to touch that files for customize the page like put the background image and icons for each widget.
How can I edit that files and please let me know about the path of that files.
Looking forward to hearing from you soon
Thanks for your help!