I only listened to a little of this, but Key of Db is correct, first line after short intro is a 2-5-1 to Db chord, then from what I listened it was just basically 2-5-3-6 and over again...Not including bridge/chorus or any minor chord variations...
short ex., on 2-5-3-6 in Db
Eb/
Eb/Gb-Bb-Db-F - Sun
Ab/Gb-Ab-C-Eb - shine
Gb/
F/...
...Hold F/Ab-C-Eb - Moon
Bb/Ab-Db-F - light