Fixing "HTML->Text" imported margins?

To reproduce this problem:

Notice that this web page has ad bars on both the left and right? Well, look at the text file that Scrivener creates. Probably because of the ad bars, it places the text in the center of the text window. And this text cannot be rejustified. At least, I couldn’t edit the text in order to shift it to the left, and I could find no way mentioned in the manual to change the margins, whatever they are.

So is there any way to eliminate these margins, either during or after the import?