An idea came to my mind this morning

Currently, ipboard does not allow us to change in the ACP the group icon per theme. I mean, for the same group it's icon will be different on theme 1 and them 2.
I've modified my groups color and i can use different ones per theme in the custom.css like this :
.staff {
background: url(https://i.imgur.com/1QJprWI.gif);
color: white !important;
text-shadow: 0px 0px 1px #0a0a0a, 0px 0px 1px #ffffff, 0px 0px 1px #ffffff, 0px 0px 1px #ffffff;
background-position: right 0px;
}
and in your user group name : <b><span class='staff'> .
I've found the code line in PostContainer :
{{if \IPS\Member\Group::load( $comment->author()->member_group_id )->g_icon }}
<li><img src='{file="$comment->author()->group['g_icon']" extension="core_Theme"}' alt='' class='cAuthorGroupIcon'></li>
{{endif}}
Is it possible to set up a way to get the custom group icon in custom.css in this line ?
I apologize if i'm not in the correct forum, it can give a hook creation idea.