There is this viewport meta tag in the head that is a bit different than what you usually see, but that may not even be it.
If you try resizing the browser window to max:1000px you’ll see that the grey bar goes in front of the slider ect.
There is this inline styling on that
ul#filter that kicks in only after resizing the browser:
<ul id="filter" style="position: fixed; top: 70px; right: 312px; width: 388px;" >
CSS, so may be you can customise some settings, or don’t use ‘Isotope’ on this navigation-bar, position it in the media-queries, for it is not part of a gallery (collection of images or layout boxes).