Ok try adding the below to your custom.css file. The first is for main level items the second is for the subs and BTW nice job on the site!
body #s5_responsive_mobile_drop_down_menu, body #s5_responsive_mobile_drop_down_menu a {
font-size:12pt !important;}
body #s5_responsive_mobile_drop_down_menu ul li.deeper ul li, body #s5_responsive_mobile_drop_down_menu ul li.deeper ul li a {
font-size:11pt !important;}