New ui for a web based opensource tool along with few features

Hi there, i need a new ui for an opensource web based tool along with few more features implemented. These features are in short dedicated webpages for missing tools which are not implemented into the opensource software. The new ui should be theme based, same as wordpress handles this using child themes, so to avoid to edit directly html/css etc, which will be probably overwritten once devs release a new version of the software. I was also thinking to push everything into ELK stack as another option.