That didn't fix it.
According to Firebug, it's the DIV for TabContainer1 that is inline-styled to 600px wide, but it looks like it needs to be about 580px wide, because of the indent from the left where the text is starting.
There's nothing in ProductDetails.ascx that would do this that I can find, and it's not coming from a stylesheet; it looks like a code-behind style: statement inline that's doing it.
I'll send another screen shot.
As you can see in the screen shot, the highlighted area is the problem, and it hard-coded for 600px (instead of about 580)