My topNav is moving below header on hover in Chrome only

The navigation on my site is moving to below the header when I hover over PROJECTS. This is only happening on Chrome, not Safari. It happens even when I remove all custom css from the page.

Site is here: http://www.sladearch.com/featured/

I currently use the following css to change my topNav, but the problem remains even when I remove ALL custom CSS.

 #header #topNav nav li a {
  font-family: 'proxima-nova';
  font-weight: bold;
  color: black;
  margin-right: 30px;
  top: 20px !important;
}
#header #topNav nav li a:hover {
 color: grey;
 margin-right: 30px;
 font-family: 'proxima-nova';
 font-weight: bold;
 top: 20px !important;
}

@santislade Remove top: 20px !important

What do you use the top 20px for? You can use margin top, padding top instead