bbPress.org

I am new to CSS and trying to change the formatting of my post-content div. My forum home page, and topic pages look okay but the margin in my post content page isn’t quite right. I can fix it by inspecting element and performing the change below, but then it reverts to being broke again.

I change it to this:

#bbpress-forums .post-content p {
margin: 0px 0px 0px !important;
display: block;
}
but then it reverts to this:

#bbpress-forums .post-content p {
margin: 0px 0px 20px;
display: block;
}
Any idea what I’m doing wrong? Forum is here:

http://www.planitnz.com/new-zealand-travel-forum/