Revisit Button type used on Alerts and it's hover color

[fczuardi]

Continuing the discussion started on #56 (comment)

We use on the Alert component, the Off Neutral type of the button component, that uses a blue background color on hover, and this is unspecified on the design specs.

This issue is just to keep the discussion about if we need a different type of button for the red (negative) alert, or for all of them.