Display menu at full width

Hi, I’m trying to get my menu to display at full width like the slider below it. There seems to be some padding or margin in the css preventing that, but I can’t seem to find the right selector to change it in my custom CSS. Here’s a link to the site: https://temp.www.phplonline.org/.
I am using the max mega menu plugin, but I don’t think the style rule I need to change is coming from that. Any help would be appreciated. Thank you!