You can edit the LESS/CSS for any of your themes. To do so:
Open the Code menu option on the Design tab and scroll to the Theme CSS section where all your web store’s themes reside.
Select the theme you want to edit. You will see a developer’s window open.
Immediately above the menu tabs is the Expand Editor icon which allows you to view full screen mode.
Choose to make your edits via either the Style Variables menu tab which accesses the variables file, or the Style Sheet menu tab which accesses the full theme LESS/CSS.
Once saved, changes made via the Code tab are not reflected in the Theme tab and you are locked out of editing the UI for that particular theme.
Note: You can revert to the last saved version of the theme in order to use the UI editor once again. However, you will lose any changes made to the code.
