Header resizing issue on mobile device

I modified the header image logo on this site http://www.auto-transport-supply.com to be bigger so it would fit across the layout, but when the site is viewed on a mobile phone, that header runs off the right side of the page.

Does anyone have any idea of what I can do to fix this to not have that run off the layout? I have tried many things within styles.css, but can’t seem to get this to work. I even tried changing something in the header.php file, but that didn’t work either.

I tried to contact support for this theme, but no luck. They have not responded yet.

Please let me know if anyone has any ideas.