XF 2.2 How to change the icon of a particular sub-forum?

[securedme]

For example, how do I change the icon of the sub-forum "Code modifications" in this forum?

 

[beerForo]

extra.less

Where f000 is enter the fontawesome. Where xx is, forum ID #.

.node--forum.node--idxx.node--unread .node-icon i:before {
    content: "\f000";
}

.node--forum.node--idxx.node--read .node-icon i:before {
    content: "\f000";
}