Edit the design of Volto Blocks

I want to edit the theme of some Volto Blocks, however I don't know where to put my overrides, unlike for base Volto.
I want to, say, change the position of the toolbar of the table block, because by default it is fixed at the top. That means in order to add a new row or column you need to scroll to the top of the table, which is quite cumbersome, especially for large tables.
Currently I just put my overrides in a copy of site.overrides with !important to override the default. However that is most likely not the proper way, since there is probably a method similar to editing the Pastanaga theme.
So, how do you properly override the design of Volto Blocks?