You could try the below - I paid for a developer to help me with it and this is what we put in the custom CSS. May need some tweaks etc for your site.
// fix header to top #headerWrapper { position: fixed; top: 0; right: 0; left: 0; bottom: auto; background: rgba(240,242,239,0.5); padding-top: 20px; } #page { padding-top: 2PX }
// move main gallery tns down so they dont overlap the header
.collection-type-gallery .thumb-list {
margin-top: 100px;
}
// when gallery lightbox is active
.collection-type-gallery.full-view {
#logo,