Desktop responsive when making browser smaller

Hello,

I recently purchased the vantage premium and I really love the theme. However when I scrunch my browser I am trying to figure out a way to get the mobile responsive button to appear when the site is viewed when you make the browser small. My site is https://www.isharpdigital.com. If you make the browser smaller the menu bar does not look right and should see a mobile menu button. If anyone could help it would be greatly appreciated.