civicrm dropdown list not appearing on the same popup but underneath pop-up's layer
We are having the same problem and its annoying as we can't added Shortcodes. Another post from 2016 found it was a CSS conflict with Slider Revolution.

Dropdowns in the admin area appear underneath the modal window.

Using the Function snippet didn't fix the problem for us or changing the CSS.

One hack around this that works for us is:


Click the dropdown
Move drag the pop-up box to one side to see what the dropdown displays
Click the dropdown again to close it
Click the dropdown once more
Use the curser keys to select your dropdown option
Hit the Enter key on your keyboard to select the dropdown option.