.tl-slide may have overflowing content but no keyboard-operable way to scroll it when the slide contains no focusable elements

[Tanvez]

Issue Description	WCAG Criteria	Status	Category	Example	Notes
.tl-slide may have overflowing content but no keyboard-operable way to scroll it when the slide contains no focusable elements	2.1.1 Keyboard	Identified	Keyboard	ExampleLast slide, "Sponge Ware Sherd, Harvard Yard"	Firefox automatically adds scrollable elements to the focus order, other browsers need them dynamically added (when they don't contain a focusable element).