Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/16
Q:1/8=120
M:3/8
K:Bb
['B2B2d2 f4 b2', 'c2f2f2 a4 f2', 'cd cd']  
X:1
L:1/16
Q:1/8=120
M:3/8
K:Bb
 F2 | B2B2d2 | f4 b2 | B2B2d2 | cBAGF2 | B2B2d2 | f4 b2 | fgfdec | B4 :: c2 | c2f2f2 | a4 f2 | 
 b2bg=e2 | fafac2 | c2f2f2 | a4 f2 | =egegc2 | f4 :: cd |"^f" ._e2"^p".e2 cd |"^f" e2"^p"e2 cd | 
"^ff" (edede)d | e4 (de) | f2f2 dB | c2c2 eg | B2B2 cd | B4 :|  