How to change width of infotext?

I'm trying to decrease the width on both the left and right side of the module. Using Firebug, I can see where I need to make the changes and when I make them in Firebug, I get the result I want but I can't seem to figure out where those selectors are in any of the CSS files.

Below is a screenshot of the CSS elements I am referencing above. You can see that the #featured .infotext has a width of 367px. How do I change this permanently?

Width of .infotext is overall module width minus image width (calculated in PHP code of the module).

hello,
i have the same question. I tried what you said but modifying the Module Width in the Module Properties affects the whole window (text+titles on the rigth) not only the part where the text is.
So how can be only the text part modified?? or how can be the "titles part" be modified?

try "Tabs width" parameter , default is 150

Perfect!!!!!!!!!!!!! thank you!!!!!