Menu CSS – Remove Background but Keep Button Background

I have succesfully made the background of the menu section transparent using code given by the developers.

But I would like to keep the background of the buttons themselves, how do I do this? I feel like I am close.

header#masthead { 
  background-color: #f07fff;
}
.main-navigation { 
  background: transparent; 
  border-bottom: 3px solid #007fff;
}

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