I do that, here's my userchrome:
:root{ --uc-toolbar-height: 32px; }
:root:not([uidensity="compact"]){--uc-toolbar-height: 38px}
#TabsToolbar{ visibility: collapse !important }
:root:not([inFullscreen]) #nav-bar{
margin-top: calc(0px - var(--uc-toolbar-height));
}
#toolbar-menubar{
min-height:unset !important;
height:var(--uc-toolbar-height) !important;
position: relative;
}
#main-menubar{
-moz-box-flex: 1;
background-color: var(--toolbar-bgcolor,--toolbar-non-lwt-bgcolor);
background-clip: padding-box;
border-right: 30px solid transparent;
border-image: linear-gradient(to left, transparent, var(--toolbar-bgcolor,--toolbar-non-lwt-bgcolor) 30px) 20 / 30px
}
#toolbar-menubar:not([inactive]){ z-index: 2 }
#toolbar-menubar[inactive] > #menubar-items {
opacity: 0;
pointer-events: none;
margin-left: var(--uc-window-drag-space-width,0px)
}
#nav-bar {
margin-right: 90px;
}