Add in style changes for keyboard focus for sliders and buttons.
Add in style changes for keyboard focus for sliders and buttons.

The toggle buttons still exhibit some issues showing the focus outline for me in Chrome on OS X - the focus outline for a left button seems to be underneath the button immediately to the right.
cornhundred/ipywidgets,cornhundred/ipywidgets,cornhundred/ipywidgets,jupyter-widgets/ipywidgets,cornhundred/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,SylvainCorlay/ipywidgets,cornhundred/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,SylvainCorlay/ipywidgets,ipython/ipywidgets,SylvainCorlay/ipywidgets