Remove Header while keeping Menu

I’ve been trying, unsuccessfully to remove the 20px high header. It appears basically as a dead space above the mobile menu bar. The slider in the menu controls stops at 20px as the smallest. I tried code I saw posted in support ticket but it still remains visible.

.mob-menu-header-holder {
height: 0px!important;
}
.mob-menu-header-holder {
background-color: transparent!important;
}
.mobmenu .headertext {
display: none!important;
}