It's half a simile, as in Ashmann's explanantion: "cute as a button". The general meaning is "very cute indeed", but the comparison is dropped to make the listener imagine what the thing is cute as. You'd use this in a slangy casual conversation, but not in regular daily speech.
This series ran on TV a while ago: www.youtube.com/watch?v=606eK4abteQ
The main character is "beached az", which implies "beached as a whale"... errr, but he is a whale.