Creating a child theme?

Hello guys!

I’m exciting to test an open source MAS system.
I have successfully installed Mautic on my local server and i want to begin with some easy customisation for learning this awesome application.

I want to start by developing a custom theme. Does anyone have experience with this?
I already checked the documentation but it’s a little bit unclear.

I want to change some colors, icons and logo’s for the backend. I can change this in the default css/LESS but when a new update becomes available all the changes decipeer in the wind…

Is it possible to create a child theme? (I mean a custom theme that uses the default theme with a few changes…)
I’m a junior php developer but i don’t have any experience in Symfony. It’s looks a bit overwhelming to be honest.

Thanks a lot for reading my post.
Kind Regards

Jorn from Belgium