while z-indexes are important to look out for. This specific issue is sorta a known "difficulty" I won't say bug cause its not its just an issue with positioning and the Actions menu.

If you have HTML skin then find [ACTIONS] TOKEN in the container and change it to [DROPDOWNACTIONS] and make sure you do the same in the xml file.

If its ASPX skin then find control Actions and do the same.

To make a container the default, all you do is go into site admin - site settings and pick the skin / container to use there. That will set your default which will set the admin controls to as well. Note the page level settings override this one, but it stands for anytime <none> is selected as skin / container.