Gallery Image Appearing Behind Menu Bar

Hi

I have a problem with the gallery. All the top thumbnails or first row thumbnails are giving me problems. When I click any of the top thumbnails to have a view of the picture, the picture opens up behind the menu bar, which means a portion of the picture is covered by the menu bar. This happens before I scroll down. When I scroll down the other pictures are fine as the menu is way too far on the top. Please assist, check this link and click the top thumbnails and see what I am talking about https://woodgrain.co.za/doors/