Enabling the DS
In order to enable the DS to modify a theme, edit a quiz with the theme you want to modify, go to General Settings, and click on the Advanced tab:
Enable the DS by clicking on Use Design System:
Once the DS is enabled, you will work on a forked branch of the theme so any updates including fixes to the main branch will not be applied to your branch.
When the DS is enabled, a new tab with the DS builder will show up: