Unable to change background color in MenuBar on hover in Vaadin 8.8.6

I have tried every selector:

.v-menubar { }
.v-menubar-submenu { }
.v-menubar-menuitem { }
.v-menubar-menuitem-caption { }
.v-menubar-menuitem-selected { }
.v-menubar-submenu-indicator { }

And i can not change the BLUE background color that the menubar component shows when I hover over the menu item. Can someone give me an example how I can change the mouseover color in the menubar component??