In this picture:
![actual][1]
How do I remove the background of the highlighted area to make it look like this:
![expected][2]
There isn’t an available theme option in Lock 10 that would allow you to configure the background you mention.
In addition, although you can try to provide CSS overrides to accomplish that goal, we recommend against this approach as it’s a brittle workaround in face of possible changes in future Lock versions. Having said that, if you do decide to go down the route of providing CSS overrides you should read the available documentation on that subject.