As per my knowledge there is no default option like this. But I am trying some custom css for doing this. I hope this may help you.
Use this custom css
header#sp-header {
position: absolute;
background: transparent;
box-shadow: none;
top:38px;
}
div#sp-top-bar {
position: absolute;
background:transparent;
top: 0px;
left: 0px;
right: 0px;
z-index:2;
}
#sp-header.header-sticky {
background: #000 !important;
}
Path towards custom CSS: Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.