Show overlaps and empty days in the monthly calendar 4.0

When checking the monthly calendar 4.0 at the end of each month, we also check whether there are any overlaps. Although there is also the Notifications item, if someone enters an overlap "willfully" despite a warning, no notification appears. In MK4.0, it would be nice if days on which overlaps exist were visually marked in color or in some other way. Days on which target time is stored but no time/absence has been recorded should also be visually marked. Currently, they are simply gray, which is not particularly noticeable.