The problem is that you have shifted #navMainWrapper, so its right edge is now 68px farther than it would normally be. Give it a padding-right of additional 68px or so and you should be ok.
Actually, margin-right: 68px; does the job even better, as the invisible wrapper volume no longer sticks out beyond #mainWrapper on the right edge, and will not affect small-screen displays.
margin: 0 6.8em 0 0; /*compensate for relative position*/
padding: 0.5em 0.2em;