first this is in no way an easy thing to do in prosilver. if you are not really good with html & css I would not even attempt it.
Second if you really want to do this I need to ensure that you are making a new custom theme.
Third you also need to be doing it properly by only making changes in a new custom.css file.
Lastly I would recommend that you just completely recreate the entire forum and topic sections from scratch. This is why I said its not easy as otherwise it will take a lot of weird and unapparent tweaks. I would start by finding a theme that has already done this and copy it. or you could use the code I worked up for the new theme.
if you still want to go through with making the changes then google chrome inspector is your friend but your gone have a bad day