It always seemed to me that there was something interesting going on in the chord progression of this song. So I looked at the chords of the verse:


I'm think the song is in the key of B major... but I'm not entirely sure what to make of it. The C# major chord seems to be borrowed from the parallel lydian mode, but then what's the Em doing there? Where is that from?

I'm very confused. Can anyone help me make sense of this?
Even if they didn't use theory to write it, there's likely a theoretical explanation as to why it sounded good. I'm trying to find that explanation.