adding a tooltip in IPython buttons
Merge pull request #6605 from SylvainCorlay/tooltip

Adding a tooltip in IPython buttons
Add semantic classes to top-level containers for single widgets

This makes it much easier to customize all widgets of a certain type using
CSS.  For example, to change just the IPython widget selects, a CSS
rule like .widget-select select {...} should work well.
Merge pull request #6609 from SylvainCorlay/widgetcssclasses

Add semantic classes to top-level containers for single widgets