ng-zorro-antd/menu/style/patch.less

An enterprise-class UI components based on Ant Design and Angular

.ant-menu-submenu.ant-menu-submenu-placement-bottom {
  top: 6px;
  position: relative;
}

.ant-menu-submenu.ant-menu-submenu-placement-right {
  left: 4px;
  position: relative;
}

.ant-menu-submenu.ant-menu-submenu-placement-left {
  right: 4px;
  position: relative;
}