add tooltips to the top-level buttons
Merge pull request #2682 from devoncarew/devoncarew_tooltips

add tooltips to the top-level buttons
Merge pull request #2714 from ussuri/un-deliverChanges

Un-deliverChanges() #1: get rid of the toxic addEventListener()
Mechanical change from @published to @PublishedProperty(reflect: true) for all attributes

This turns on property-to-attribute value synchronization, now turned off by default. That is required for the CSS to see the changes applied to properties programmatically.