The invisible code selection highlight is a really big issue at the moment. Absolutely love how beautiful this is otherwise.
I fixed this temporarily so I could work by modifying this bit in your addon:
span[style="background-color: rgba(0, 0, 0, 0.2);"]{background-color:transparent!important}
to:
span[style="background-color: rgba(0, 0, 0, 0.2);"]{background-color:red!important}