For the intro, chorus and they just play power chords.
Each is strummed four times.
C---G---A---F
At the very end the last chord is E
Verse.
G---A---G---A---G---A- G F
Bridge. (no power chords)
G G D7 G C D7 G-
The end picking 4x after 4x
[ Tab from: https://www.guitartabs.cc/tabs/o/ocean/back_then_tab.html ]
e|--------------------------|------------------------------------------------|
B|--101-101-101-303130------|--578-873---------------------------------------|
G|-2---0--------------------|----------8-------------------------------------|
D|---------2----------------|------------------------------------------------|
A|--------------------------|------------------------------------------------|
E|--------------------------|------------------------------------------------|