There is a small 5px of padding on the bottom of the #header…..but most of that space is actually from the navigation links. They have 14px of padding on top and bottom. Here is the ID for those links – #nav .genesis-nav-menu a ….that can be found around line 1000 in your css. You’ll have to adjust the top and bottom padding of those links in order to see a difference. You’ll also have to adjust the rem as well.