Craft a musical piece that abides by the prescribed structural guidelines and the given theme.
X:1
L:1/8
M:2/4
K:Bb
['cc g2- g4 fg/f/ed/c/']  
X:1
L:1/8
M:2/4
K:Bb
 cc g2- | g4 | fg/f/ed/c/ | bgcf/b/ | g4 | cc g2- | g4 | fg/f/ed/c/ | bgbg | c4 |]  