Set Preview-List component background to only set background-color

Summary

Currently the CERN theme overrides the Preview List component because instead of setting the background-color of the image, it sets the background and as a result it overrides the CERN logo.

Steps to reproduce

1. Add a Preview-List component without image.
2. Notice that the background color overrides the logo

Possible fixes

Change background to background-color

Related issues

• web-team/drupal/public/d8/modules/cern-components#17 (closed)