Custom CSS File Column Background Image

Hi,
First thanks for the great theme very good work. But I have one big Problem have done Productpages with Columns and in one column there is a Image Gallery. I want to costumize the Background of the image gallery and i have done this in the custom css file with this

div.flex_column.av_one_fourth.avia-builder-el-16.el_after_av_three_fourth.avia-builder-el-last {background: none repeat scroll 0% 0% #d1c39f;
padding: 7px;
border-radius: 5px;
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
border: 2px solid #800000;
height:400px;
Now the problem If I change this parameters it changes this on every site of the whole web page where this column element “avia-builder-el-16” is used. Thats horrible i really hope someone can help me out.
Or is there a other way to put images or colors in background of culomns individual to every site and formation.
Thanks and kind regards