[A11y] SiteImprove a11y issues on timeline view page

[Dananji]

Description

The timeline view page including the timeline settings modal at https://timeliner.dlib.indiana.edu has the following a11y issues when scanned with SiteImprove,

Success criterion	WCAG 2.1 Level	Error	Relevant HTML element
4.1.2 Name, Role, Value	Level A	Button missing a text alternative	Color picker button in annotation edit form
4.1.2 Name, Role, Value	Level A	Form field missing a label	For each hh:mm:ss input (textbox) in start/end time input fields in the annotation edit form
4.1.2 Name, Role, Value	Level A	Role with implied hidden content has keyboard focus	Volume slider element
4.1.2 Name, Role, Value	Level A	Button missing a text alternative	Background color picker button in the settings modal and bubble height slider thumb button
4.1.2 Name, Role, Value	Level A	Hidden element has focusable content	Edit annotation buttons hidden underneath the settings modal
1.4.3 Contrast (Minimum)	Level AA	Color contrast does not meet minimum requirement	Download this timeline and Start this timeline over buttons that hidden under the modal overlay
4.1.2 Name, Role, Value	Level A	Form field missing a label	Slider for setting the bubble height

Part of avalonmediasystem/avalon#6435.

Done Looks Like

• SiteImprove doesn't show any Level A/AA a11y issues when the page is scanned with all of its elements
  • timeline view
  • timeline view with the edit bubble/marker form opened
  • timeline settings modal