Yes, this rule prevent the menu underlay from showing:
.overflow-menu:after,
.header__underlay {
display: none;
}
An option is to change it to:
.overflow-menu:after,
.header__underlay {
/* display: none; */
max-height: var(--header-height);
}
I’ve shared the full updated code at Horizon Submenu/dropdown alignment & carat - #7 by tim_tairli