five-for-the-future/themes/wporg-5ftf/css/components/_wporg-header.scss

#wporg-header {
	@include breakpoint( $breakpoint-tablet ) {
		ul li.current-menu-item:after,
		ul li.current_page_parent:after,
		ul li a.current ~ .uparrow {
			body.blog &,
			body.search &,
			body.single &,
			body.archive & {
				border-bottom-color: #f7f7f7;
			}
		}
	}
}