Prevent .retina() from overriding other background attributes.

Review Request #9844 — Created March 28, 2018 and submitted — Latest diff uploaded

Information

Djblets
release-1.0.x
d5aa886...

Reviewers

The new .retina() LessCSS mixin was setting background: instead of
background-image:. This caused other CSS rules, like
background-repeat:, to be overridden, regressing behavior.

It now sets background-image: explicitly.

Tested with existing icons. Didn't see any regressions.

Tested with the Intercom chat bubble icon on RBCommons. It was no longer
repeating weirdly.