active tab panel not visible in high contrast mode

[Becky Gibson]

We need to distinguish which is the active tab panel when in high contrast mode. Accordion container makes the distinction by making the title text bold - tab container could do the same thing.

[bill]

Or alternately, invert the text as it's done for the (label for the) active pane in AccordionContainer? in soria (see ​http://archive.dojotoolkit.org/nightly/dojotoolkit/dijit/themes/themeTester.html?theme=soria), and for the active menu item, and for the active day on the calendar.

(I'm not sure if it would look good for tabs or not, but it almost seems like a standard for dijit)

[Becky Gibson]

Note: whatever method is used, be careful about changing size of tab

[Becky Gibson]

(In [10753]) fixes #4561 - added dijit_a11y .dijitTabChecked style to use a dashed border for active tab in high contrast mode. Also had to add dijit_a11y .dijitTabInnerDiv to remove left solid border when in high contrast.