Replacing vertical background gradient with single color, as no
faux 3D gradients are part of current style guide.
Change-Id: If98a6cb22a9551a5d69d782759eadd5cec7e0efc
Replacing all colors with current WikimediaUI palette ones.
Also:
- changing two files over to LESS in order to
- make use of central gradient mixin instead of one with
unnecessary vendor extensions and
- concatenating selectors in one occurrence.
Bug: T174237
Change-Id: I5d302f29b079f6abdba5abf3b58d6ba254e1a4ac