Visible focus indication is lost when Zoom buttons are disable

[Tanvez]

Issue Description	WCAG Criteria	Status	Category	Example	Notes
Visible focus indication is lost when Zoom buttons are disabled.	2.4.7 Focus Visible	Identified	Keyboard	<button class="tl-menubar-button" type="button" aria-label="Zoom out" aria-description="Show more than 1730 to 1970" disabled="true"><span class="tl-icon-zoom-out"></span></button>	Consider using aria-disabled="true" instead of disabled and a different visual treatment of disabled buttons. Or don't disable at all; "goback" and "goend" buttons aren't. Maybe change aria-description to indicate zoom limit has been reached.