#sidebar_header {overflow:visible;}
#sidebar_header .header-widget {padding-bottom:0;margin-bottom:0;}
yes and this is because you used the Horizontal header widget area. You must have read a post I made on the Weaver forum because you added
#sidebar_header {overflow:visible;}
#sidebar_header .header-widget {padding-bottom:0;margin-bottom:0;}
which is to remedy an overlay issue with that widget area, but because you are actually bringing your menu up over the widget area, it does not suffice.
The best would be to simply use the header image. You can use the same image and check the option in MAin Options > HEader > Header Image > Use actual image size
Just getting rid of the Header Horizontal Widget area and putting your image as the header image may be all you need, or we may need to re tweak the menu.
It will be easier to see once you have the header image in place