On a front page I have a main menu being modified by Nice Menus module. There is also a Views Slideshow display in a different region. When drop-downs are triggered from a Nice Menus item, the drop-down doesn't display properly over the Views Slideshow. (see screen capture - dropdown from "All Applications & Forms") It seems to go behind it. Doing an almost identical thing in Drupal 7, I didn't have this issue. How can this be fixed?

Comments

This looks like a problem with z-index. You could write custom code to fix it yourself in your sub-theme (if you have one). But, if you could figure out which module is responsible for the problem, you could file a bug report and hopefully get some help. 

Nice Menus - https://github.com/backdrop-contrib/nice_menus/issues
Views Slideshow - https://github.com/backdrop-contrib/views_slideshow/issues
Backdrop Core - https://github.com/backdrop/backdrop-issues/issues

Using the forum is fine for a problem like this, but if it's a bug it might be better to post something in respective issue queue. If your not sure which issue queue, try to provide more information about what is happening and we can try to help you figure out which module is responsible.