UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.116 Safari/537.36

Example URL:
http://codepen.io/redsunsoft/pen/yaOoam

Steps to reproduce the problem:
1. Just load the codepen
2. On some displays, the ".background" div covers the full area, on other displays, it does not.  See video of "white vertical strip" on left side of page. 
3. 

What is the expected behavior?
".background" should cover the entire area on all displays

What went wrong?
A white vertical strip (looks like margin: 10px) shows up on some displays.

Does it occur on multiple sites: N/A

Is it a problem with a plugin? No 

Did this work before? N/A 

Does this work in other browsers? Yes 

Chrome version: 53.0.2785.116  Channel: stable
OS Version: OS X 10.11.6
Flash Version: Shockwave Flash 23.0 r0

https://youtu.be/FT3d2gvFFwQ