Remove the left navigation bar in SharePoint 2013

I am using the code from this page to remove the left navigation bar on some of my SharePoint 2013 pages.

<style>
.ms-core-navigation { DISPLAY: none }
#contentBox { margin-left: 0px }</style>

But, while I find the above code removes content, I still see a grey box for the area and the rest of the page content does not move over to replace it.

Can you help please?

Dave Englund