User styled posts?

Please excuse me for revisiting this. The OP in this thread was the one who created our Community, but is no longer in that position. I admit to being clueless and please excuse me if I’m out of line here, but is there something we can do that will allow users to use .css in threads to make styled opening posts for their topics?

The recent update to close the exploit killed the coding they were using.

I’ve tried to make sense out of what I’ve read here, but it’s a bit beyond me. Is it possible to create a theme that will allow users to use .css in posts without ruining security?