This seems to be intentional. https://github.com/joomla/joomla-cms/blob/4.0-dev/templates/cassiopeia/scss/blocks/_layout.scss#L33 there's a 4rem top and bottom padding which means top-a and top-b there's 8rem padding.

@drmenzelit Comes from your commit here 6ad0537 - not sure if you want to adjust or if it's expected to you

We had a big discussion about white space between modules... we can replace padding with margin, then it will not sum up between containers

There shouldn't be any padding or margins. It's using css-grid, so it should be dealt with by grid-gap

I see... grid-gap for the body is set to 0 1em

but changing it will have other consequences... for example it will add a gap between header and banner

Any update on this?

Closing with PR #33310