Border around calendar

You will need to add CSS for this.

For the dates you could use this:

.simcal-day { border: 1px solid #000; }

Just swap out the hex code with the color you want to use.

For the border around the calendar you could try this:

.simcal-calendar-grid { border: 1px solid #000; }

You will need to add these to the bottom of your theme stylesheet.