Menu bar popup background/border color


I’m trying to implement all-black navigation menu and I’ve almost done it but still there is a white frame aroud menu items:

I’ve tried to change various classes/parameters in CSS around this element but without any succeess.

<div class="v-menubar-popup" style="margin-left: 0px; margin-top: 0px; left: 880px; top: 37px; z-index: 20000; position: absolute; overflow: visible; visibility: visible;"><div class="popupContent"><div tabindex="0" class="v-menubar-submenu v-widget borderless v-menubar-submenu-borderless"><span class="v-menubar-menuitem"><span class="v-menubar-menuitem-caption">TBD</span></span></div></div></div>

Could please somebody advise how I can reach that stubborn frame :)?

Checkout this Video
The Example in the Video is about Buttons but you can transfer the knowledge and use
this mixin
this one
to style the bar and the popup

Eventually I styled it using:

      background-color: #414B56;