Arms and the Man can be described as a modern play, even though it was first produced in 1894 (and followed the Naturalistic characteristics Shaw used in writing), by looking at the themes focused upon in the play.
One theme highlighted in the play is the romanticism of love. regardless of what era you live in, romantic love is always prevalent. Many people have been charged with falling for the wrong person. This idea has traversed time.
Another theme which could be recognized as a modern theme is class discrimination. As forward thinking as ones society believes it to be, class discrimination is still prevalent. It seems that people have always, and will always, look down on those they deem below them.
Finally, the theme of idealism verses realism has been a topic upon the minds of even the greatest people for centuries. Literary and artistic movements have developed around these ideals and still bring about great conversations.