Here’s a formating suggestion for the calendar GUI…
Currently, the actual dates in the full month mode appears in a coloured bar above the each date’s text box. However, when an individual box is selected, the date is not highlighted and its therefore not obvious whether the applicable numerical date is either the one above or below the text box. This can result in accidentally entering an event on the wrong date (off by a week)—this has happened to me several times therefore the GUI is not intuitive.
Ambiguity could be eliminated by bolding the margin line around the entire box (including both text and date) whenever that date is selected. Otherwise a great product–keep up the great work!!
Well, the date is always at the top so there should be no confusion. 
I wonder if this can be changed in the Theme. Maybe someone into theme editing can comment.