Widget theme
Widget themes has few sections. I'll try in short term describe what you can do in each of them.
Status widget style
Here you can change main widget attributes. Like logo etc.
tip
Some of these attributes are quite old and not used anymore. They will be removed in old version.
Widget container
Here you can change general outlook of widget. Like borders padding etc.
Messages style
Here you can change how message style looks like for visitor.
Need help widget
You can change how need help widget looks like.
tip
This is not yet supported in new a widget.
Chat widget
Here you can change default text in widget itself.
Custom content
You can write custom HTML above start chat form fields.
Custom CSS
If you want to style form directly using CSS you can use this section.
Custom bot style
You can change default bot buttons style.
Notification
If you are using notifications functionality you should set logo and notification details here.
Permissions
In order operator to be able edit themes, set default theme he has to have this permission
'lhtheme', 'administratethemes'