Andrew, if your mobile menu is overwhelming on a Mobile device then it means you have not designed your website with Mobile navigation in mind. I would suggest you redesign your website navigation if a large number of people are going to be viewing your site on mobile.
PS. It is pretty common these days to see a phone screen completely full (and more) by a mobile menu. If your traffic from mobile phones is expected to be low, I wouldn't worry about it. You can use the above CSS I have provided and the mobile menu should only show on Phones and may be Mini-Tablets, but your full navigation bar will be seen on full size Tablets without the sidebars if you customize it that way like I have on another site.