Increase Max Width of Page Content Area Image on No Sidebar Layout?

Hi, using the Simple Catch free theme and really like it. Is it possible to increase the maximum width of an image in the content area of a page, for the no sidebar layout? I am currently trying to use a wide image at top of page (http://beachbirthdayparty.com/contact/) to look like a sort of header - I want the image to be same width as the menu bar (page layout is no sidebar). The image is sized at 978px wide, and I already added the below custom css to increase the content area width for no sidebar to 978px, thinking that was the issue, but the image is still not as wide as it needs to be, it seems that it's being reduced. Is there a simple CSS code change that will fix? .no-sidebar #primary { width: 978px; } I'm currently using a Child theme I created based on Simple Catch theme. Also still newbie learning at CSS if you haven't noticed :) I thought maybe I need to adjust a max-width img property somewhere (?), but couldn't find any CSS code for max-width in the Simple Catch stylesheet, atleast not in the content-side-bar.php, or content.php. But not even sure if that's the CSS code I should be looking for or need to change?