.tl-timenav is focusable but visible focus indication is poor

[Tanvez]

Issue Description	WCAG Criteria	Status	Category	Example	Notes
.tl-timenav is focusable but visible focus indication is poor (Chrome) or absent (Firefox, Mac Safari).	2.4.7 Focus Visible	Identified	Keyboard	<div class="tl-timenav" tabindex="0" role="application" aria-label="Timeline navigation " aria-description="Navigate between markers with arrow keys. Press "Home" for the first and "End" for the last markers" style="height: 304px;">	Using a negative value for outline-offset may help.