Gedshow should work well with most themes, however, some themes over-ride the button settings in Gedshow. Please let me know of any misbehaving themes so that I can make changes to gedshow to work with that theme.
Themes that are known to work well with Gedshow are 2016, Astra, Bard and Suffusion. All except Suffusion are available from the WordPress Theme Repository and Suffusion is available from GitHub.