Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
Q:3/8=90
M:6/8
K:G
['BGB AFD G3']  
X:1
L:1/8
Q:3/8=90
M:6/8
K:G
|: d3 BGB | c3 ABc | BGB dBd | gdc BAG | cec B3 | AFA c3 | BGB AFD | G3 G,3 b3 dgb | a2 A dfa | 
 gfg eag | fed =f3 | ece a3 | dBd gdc | BGB AFD | G3 G,3 :|  