Blog Post > Grid Layout change background by category

Hi,

I’m using the grid layout and I wanted for each post to have a background color based on its category.
I searched in the documentation and found : https://kriesi.at/documentation/enfold/blog-post/ > Different post style for each category, which says :

“All posts added to a specific category can be styled to look different from other posts using custom CSS code. A unique CSS class name in the format “category-xyz” is added to all of the post articles.”

But it seem there is no category class name added … here are the classes I got in the <article> for an article in the “news” category.

class=”slide-entry flex_column post-entry post-entry-51 slide-entry-overview slide-loop-2 slide-parity-even av_one_third real-thumbnail”

Can you help me with this ?

I tried to had {$cats} on this line of the config-templatebuilder/avia-shortcodes/postslider/postslider.php file but without success.
$output .= “<article class=’slide-entry flex_column {$style} {$post_class} {$grid} {$extraClass} {$thumb_class}’ $markup>”;

Thanks a lot