Please share with me an app whose UI design you think has a good system for colors, dimensions, breakpoints, padding, margins, and gap spacing

Hi,
I would like to use an app that has a well design system as a reference and learn this system to use in the applications I may work on.

So since I am not a UI expert I would like to get your recommendations for an app whose UI design you think has a good system for colors, dimensions, breakpoints, padding, margins, and gap spacing.

This could be an app that you have developed, someone else has developed, or maybe a free template, so the app editor can be accessed.

I appreciate any recommendations or thoughts and thank you in advance.