Shifting Primary Menu

I am new to WordPress. I just started working on an existing website. I have been trying center the primary menu, but it is not working. So, it looks like the menu is shifting back and forth when you interact with it. Something keeps overriding the correct settings for the website and I cannot figure out what’s up. Any help would be so much appreciated. The website is based on the Retailer theme.

The site is: http://www.luxurylashacademy.com/