Hi  A_Goer,

Please use the following CSS code.:

#wpforo #wpforo-wrap .wpforo-topic-icon{
     font-size: 27px !important;
}

Don't forget to change the red marked color codes before using.

Thank you @a_goer,

I'd recommend remove this CSS code from Dashboard > Forums > Settings > Styles > Custom CSS Code textarea. I don't know why you've put it, but it makes small all wpForo icons. This is a wrong code:

[class*="fa-"] {
font-size: 12px !important;
}

Thank you