changing the margins of a specific picture without impacting all sitewide images

Hi ladies and gents,
I may need your help for a work in progress as I experience basic issues trying to change the top and bottom margins of one single element (image):
There is one single image on this page:
http://restauration-arts.com/wordpress/activites/restaurer-le-support/

When I try the following customs CSS:

.avia-align-center.avia_image.avia-builder-el-no-sibling{
margin-top:20px;
margin-bottom:30px;
}

… it alters the the top and bottom margins of other sitewide images.

Troubleshouting this should be easy, I guess, but I coudn’t find how to change this specific item CSS only. Any help?

Thx,

A.

• This topic was modified 10 years, 9 months ago by Alexoidea.