.wp-block-navigation:not(.has-background) .wp-block-navigation__submenu-container:before {
  border-bottom: 7px solid var(--wp--preset--color--secondary) !important;  
  left: auto;
  right: 30px;
}

.wp-block-navigation__responsive-container.is-menu-open .wp-block-navigation__responsive-container-content .has-child .wp-block-navigation__submenu-container {
    font-size: 1em;
    border-top: 1px solid #fff;
    border-bottom: 1px solid #fff;
    border-radius: 0;
    padding-right: 0;
}