From #27579:

It feels like having a way to set the default padding in the block's supports field instead would make it more convenient for customization purposes. In addition to true it could support an object with default values or anything that the theme.json is using.

As noted on that PR, setting default styles in the way the handbook recommends results in validation errors in the block.

As can be seen in #27582, if we set these values in CSS rather than in the JSON then when the user resets the setting, the CSS takes control, which is confusing for the user.

I agree with @gziolo that we should be able to set this in the block.json somehow.

cc @nosolosw @jorgefilipecosta