Any way to create a "Save" + "Cancel" button?

How would I alter the flow of the modal so that it incorporates a "Save" + "Cancel" button?

The flow I'm looking for is for a user to open the modal, click on a date, this date gets highlighted in a color, then they have to hit the save button to close the modal and store this date. If they hit cancel, and then re-open the modal, ideally the previous date will remain selected.