Jquery Slide effect on .toggleClass()

I am making a website for a small business I might do. Ive started with a nav bar which when I click the menu icon the rest of the nav-bar slides down smoothly. I have got this far: http://ift.tt/2jLTH5P I just cant figure out how to make it slide smoothly, I would rather it be done in Jquery (Not UI), but minimal CSS/JS is okay.

Thankyou ~Luc