Hello, yfzhang. It has been some time since your post but in case that you still need assistace I will be happy to help.

I was unable to reproduce the behavior you’re describing. However please note that the following CSS classes apply to menu items in the menu: .igdm_MenuItemVertical, .igdm_MenuItemVerticalLink, .igdm_MenuItemVerticalSelected, .igdm_MenuItemVerticalActive, .igdm_MenuItemVerticalHover. They are located in ig_res/Default/ig_datamenu.css file in your project’s directory. Therefore if you are applying custom styling to your items, you should ensure that the background color is set for the relevant classes.

In order to be able to provide more insight it will help if you can provide a small, isolated sample application that demonstrates the behaviour you are seeing.

Please let me know if I can provide any further assistance.