It Came Upon A Midnight Clear by Carpenters is in Ab at 90 beats per minute and runs 0:40 across 18 bars. It uses 26 chords — Eb, G, F#dim7, Adim7, D7, Abmaj7, Gm7, Cm, and a few more. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? It Came Upon A Midnight Clear guitar melody tab.