.wp-block-navigation .has-child .wp-block-navigation__submenu-container>.wp-block-navigation-item>.wp-block-navigation-item__content {
    background: #0e51a8;
    color:#ffffff;
}
.wp-block-navigation__submenu-container {
  position: absolute !important; /* ensures it breaks out of parent flow */
  z-index: 9999 !important;     /* higher than any other site container */
  background: #fff;             /* optional: ensures content is readable */
}