Popup div location not behaving according to settings

Hello,

First, great plugin. Setting the popup div to middle center results in it being floated left. None of the available settings results in horizontal centering for the theme we’re using. Could I send you a private link to a page that we have set up for testing? There aren’t any CSS clashes that I can see, so I’m baffled. Thank you.

https://www.ads-software.com/plugins/popup-maker/