Add a top and bottom border to the menu / navbar area

open the Customizer, go to STYLE > Components > Navbar, pick your colour by setting Border: rgba(190, 175, 130, 1) (for example), set Border Width: 15px, and select Mode: Border.

If this doesn't work add CSS and style for a bottom border

/*header bottom border*/
.uk-navbar-container:not(.uk-navbar-transparent),
.uk-navbar-transparent {
border-bottom: #ff5b00;
border-bottom-style: solid;
border-bottom-width: 12px;
}

For top and bottom border

/*header top and bottom border*/
.uk-navbar-container:not(.uk-navbar-transparent),
.uk-navbar-transparent {
border-bottom: #9E9E9E;
border-bottom-style: solid;
border-bottom-width: 1px;
}

.uk-navbar-container:not(.uk-navbar-transparent),
.uk-navbar-transparent {
border-top: #9E9E9E;
border-top-style: solid;
border-top-width: 1px;
}