css question

I have just installed the Q&A plugin here:

As you can see, it needs a little work on the css (margin on the left), but where would I make those changes?

I've tried various places in general.css (uploaded to my theme folder), but I don't seem to be gettign the right place.

Also, it seems to have broken the theme somehow. The login section should be in the sidebar on the right, below the map.

I managed to get the left margin to change only by editing the css file in the plugin, but when I do that, I don't get the full section for the question, it cuts off on the right, even if I make the size much narrower.

For example, the size of the area is 620 pixels. I've made the margin on the left and right 10 pixels, and the width 600 pixels, but it is cut off. However, if I make the width 300 pixels, it is still cut off.