Horizontal over flow issue when using off-canvas mobile menu in Oxygen 6

[janknop]

Mobile menu causes horizontal overflow to stretch wider that the view port causing horizontal scrolling in Oxygen 6.

Steps to reproduce the behaviour:

1. Use off canvas menu
2. Change the view port to mobile size (or whenever off-canvas kicks-in)
3. You can now scroll horizontally
4. The bug only fix is to set overflow-x in CSS with !important attribute.

This is the same issue that was causing problems in the previous version of oxygen.