Accessing the CSS compatibility tooltip via keyboard navigation isn't possible. There are a number of issues to address:

• The tooltip should not be accessible with just hover events. The user should be able to have the tooltip shown when the compatibility icon is focused when tabbed to.
• There has to be a better way of showing information for which browsers are not supported. Right now, the user has to hover their cursor over a browser icon, which will display a tooltip showing the version.
• The "Learn more" is not accessible from the keyboard.