dropdown menu...

Hi,

My navicon rolls out a dropdown menu at tablet view. I would like the solid color in the background, behind the menu links to span the screen from edge to edge with that background color so user's eye zeros in better on the menu vs. it being presented in a slim vertical presentation.

Not sure what property I need to add to get this effect? I tried margin: 0 auto;  - but that did nothing. (using Bootstrap)

Thank you!