blog archive margins (featured image & excerpt)

Hi,
I've a problem with the margins of the featured image (bottom margin 1em instead of 2em) and the excerpt (top margin 1em instead of 2em) of the posts of an archive.
I'm using the 4 columns view.
this, for example, does nothing:

.post-image-above-header .inside-article .post-image {margin-bottom:1em;}

I already checked the forum, found some users with a similar problem, but couldn't find a solution.

In the private information you'll find a link to an example.

thank you!
Davide