CSS for fixing Appointments+ "legend" display

On this page https://bluechaircounselling.co.uk/room-booking/ there's a booking calendar and under that, there's a legend ("Free", "Busy", "Not possible") which has a border around. On Firefox that border is properly displayed around the legend table (left, right, top and bottom). In Chrome browser, there's only left and top border while it should be around like in Firefox (all edges).