Use transparent colors for Skeleton loader
When adding the skeleton loader component to our Figma library (gitlab-design#888 (closed)), we decided that it would be better to use transparent colors instead of the current opaque colors. You can see the design specs here (the gradient is not detailed here): https://www.figma.com/file/qEddyqCrI7kPSBjGmwkZzQ/Globals-beta?node-id=2844%3A0
Transparent colors allow for a better contrast regardless of the background. Additionally, this is a good step towards having both a light and dark UI.
||Black 16% opacity|
|Pulsing gradient wave (
||Black 8% opacity|