Try this in "enter site" CSS. The color are the 22's and transparency is the .20. .sm-page-layout-region-header {background:rgba(22, 22, 22, .20) !important} If you want a fine border at the bottom add this. border-bottom: 1px solid #999;
Absolutely go into your customization again and remove the CSS you added: .sm-page-layout-region-header {background:rgba(22, 22, 22, .20) !important} And the header should be totally clear.