Make sidebar colors the same

Right now our contextual navigation sidebar and our issuable sidebar are two different colors. The color difference is very slight and it looks unintentional. We should consider making them the same color or increasing the contrast between them.

Proposal

Make sidebars use the same background color by changing the new contextual sidebar to match the others (#fafafa)

cc @pedroms @cperessini

I am in favor of making them the same color. The different shades do not seem to convey the message that was originally intended with the design.

I'll leave it up to @pedroms, though, since he has a better understanding of what went into this decision.

mentioned in issue #37828 (closed)

@pedroms is going on vacation soon. Lets make them the same color since there is an agreement.

changed the description

added UX ready label

assigned to @tauriedavis

mentioned in issue #35740 (closed)