Calendar Day Headings don't line up

On the calendar, the appointment Day (Sun,Mon,etc) doesn't line up with the number days (1,2,3). Where in the CSS can I adjust the margins/padding for the headings? This is only an issue when viewing from an iphone/android phone. My theme is responsive, and I'd like this to look presentable in desktop and mobile.

http://ameliasalon.com/in/make-an-appointment-2/