You can use keyboard navigation to open the calendar widget to select a date and you see the focus on the calendar icon (blue background with a black box-shadow). But when you click to disable the date, as in "Course end date" in course settings for example, then the focus should be removed on the calendar icon, because you can't use it if the date functionality is disabled. 

There is also a focus with the mouse, on :hover for example, which change the color icon and that should not be the case when the date is disabled.