A theme is basically a central topic ,subject or concept,the author is trying to point out not to be confused with whatever messege,moral or commentary it may send or be interpreted
A theme for game pairs requires xml and web development skill and the use of inkscape.
Firstly,I made the images in .svg format using inkscape .Then,I connected all the images with the desired theme using xml .Most importantly after making the xml file it has to be saved in .game extension .
Then, simply the file is to replaced to .pairs.tar.bz2 .Have a look at it this link for reference
http://kde-files.org/content/show.php?content=152174
http://kde-files.org/content/show.php?content=152203
http://kde-files.org/content/show.php?content=152203
Hope this helps!
Cheers!!