Not sure what you mean by 'line'.
To go from a button to a surrounding panel you'd usually use a component query.
It'd be something like:
Note that this is not a CSS query, as mentioned in your question.
var panel = button.up('panel');
If you can't accurately identify the target panel using its xtype then you may need to add an arbitrary marker property to the panel just for query purposes.
There are various alternatives to using a component query. Capturing the parent panel in the closure of the button handler is one.