Stumped - can't seem to increase the width of an image or text container

Hi Everyone-

I'm hoping someone can help solve an issue I've been having with a new layout to a site I've been running since 2004 (www.cygnus-x1.net).

The issue is on this test page: http://www.cygnus-x1.net/links/rush/new-layout-2017/hold/

The entire page functions perfectly when scaling the size of the browser window. The width of images, and the main 'Welcome' text box all increase and decrease as expected. However both the main C-X1 logo at the top of the page, as well as the 'Welcome' text box will not increase beyond 992 pixels wide, even if the browser is large enough to contain a great er width while maintaining all of the border padding.

This template, and corresponding CSS code, was created for me, and I'm afraid I'm not terribly well versed in CSS. However I have gone through the style.CSS file, as well as other CSS files, identified where the calls are for both the logo image and text box, and I see no obvious code that restricts the width of these components to 992 pixels (or approximately that width).

I'd really appreciate it if someone could take a look and point out the error of my ways

The Style CSS file can be found here: http://www.cygnus-x1.net/links/rush/new-layout-2017/hold/css/style.css
Another CSS file which I believe may also be in use is found here: http://www.cygnus-x1.net/links/rush/new-layout-2017/hold/css/dg_responsive.css

And, of course, the source code for the main page can be found via the original link above.

Thanks in advance for your help.