Investigate background-image issues
https://github.com/brainly/html-sketchapp/pull/109 gave us basic support for background-image's and it works great on most pages:

before:
<img width="758" alt="amazon-before" src="https://user-images.githubusercontent.com/985504/41361325-10ec7ce4-6f2f-11e8-8c87-6aa634b7278e.png">

after:
<img width="796" alt="amazon-after" src="https://user-images.githubusercontent.com/985504/41361324-10cab370-6f2f-11e8-90c6-1c14ca408d21.png">

but there are still a few cases where it fails e.g.

- brainly.com footer
<img width="681" alt="screen shot 2018-06-13 at 17 21 44" src="https://user-images.githubusercontent.com/985504/41361359-2ac9e7d2-6f2f-11e8-83cc-7781ecb67353.png">

- google.com search by voice icon
<img width="723" alt="screen shot 2018-06-13 at 17 16 55" src="https://user-images.githubusercontent.com/985504/41361393-3cb7f6a0-6f2f-11e8-83cc-7cfee1a30d4a.png">
