Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/4=200
M:4/4
K:D
['gfeg FGA=c EFGg']  
X:1
L:1/8
Q:1/4=200
M:4/4
K:D
 A2 |"D" dfaf"A7" gfeg |"D" fdAG"D7" FGA=c |"G" BGFG"Em" EFGg |"D" fdec"A7" dcBA | 
"D" dfaf"A7" gfeg |"D" fdAG"D7" FGA=c |"G" BGFG"Em" EFGg |1"A7" fdec"D" d2 :|2"A7" fdec"D" defg |: 
 a2 fd dfaf | dfaf bagf |"C" gfge =cege | =cege agfe |"D" a^gaf dfaf | dfaf bagf | 
"G" gfef"Em" gbag |1"A7" fdec"D" defg :|2"A7" fdec"D" d2 |]  