I'm trying to create a new ExtJS Theme, so I read few guides to do it.
I wonder if there is a way to add a CSS variable which is not already available.

For example, I'd like to add a text shadow and a box-shadow on the buttons but in the file "resources/themes/stylesheets/ext4/default/variables/_button.scss", there is no property like "$button-default-box-shadow".

What is the right way to do something like this ?

Thank you for your help.