Tested on the current ExB Dev Edition Release (1.15 as of posting this)
The keyboard's focus CANNOT move from the widget controller pane into a layer widget. This is huge, no layer widget is keyboard accessible in conjunction with a widget controller.
The pane for an active widget has a close button and a collapse button, the style's color is applied to these buttons and fails the minimum color contrast standard. Assign these buttons white or let suer's assign them.
WCAG 2.1 AA compliance is federally mandated of all state and local government web content. In order to use ExB, government employees need to be pushing for accessibility enhancements.