localsports on "HTML/CSS Help"

I installed a plugin that has a front end editor. I am trying to make the edit box that the plugin uses longer. (the text area where a user would input his/her post.

Be default, it appears that it is set to only 100px. I would like to make the default 500px.

I think this is the code where the default height is located:

<iframe id="new-post-desc_ifr" src='javascript:""' frameborder="0" allowtransparency="true" title="Rich Text Area Press ALT F10 for toolbar. Press ALT 0 for help." style="width: 100%; height: 100px; display: block;"></iframe>

So in my Quick CSS box I put:

.new-post-desc_ifr {
height: 500px;
}

and then I also put it in as an id selector:

#new-post-desc_ifr {
height: 500px;
}

but neither will work. Any help would be appreciated.