Aligning to WikimediaUI style guide by replacing colors with
standard color palette equivalents, merging close colors
(ex: `#E6E6E6` & `#eee` become `#eaecf0` ) and slightly increase
contrast on a few to meet WCAG 2.0 level AA criteria.
Also:
- following other code bases like MobileFrontend or OOjs UI in
using `border-radius` property instead of obsolete mixin
- removing non-existing browser vendor prefixes in mixins
- removing non-used Less variables
- bringing CSS/Less code closer to coding standards and
- simplifying Less code where applicable
Change-Id: Icb936e14ff613471ea1da6df6341ec1b0543cfaf
Replacing colors with ones from current WCAG 2.0 level AA compliant
color palette. Also improving SVG files by svgo optimization where
easily applicable and cleaning up some minor Less shortcomings.
Bug: T149769
Change-Id: I3d46c95a61112ba808c6ec664a95c94e9cb42c5e
