[Request] changing styles on the default theme

can the team show an example on how to change a style of a component correctly ? like table element for example. 
it is unclear what is the source of truth - the scss ? the :root css vars ? and how to override correctly without masking style on top of another style. 

does not have to be on the main branch - but i think there should be a reference example about the new. 
much appreciated. 🙏