The template builder has several features to design your templates. You have the possibility to add illustration layer from the component library.
In this library you will have the choice to add an element of one of these components:
Feather - Open source icon
Twemoji - Open source emoji
Material icons - Open source icon
Undraw - Open source illustration
Add an illustration
Click on the more button (+) on the top bar
Click on "Illustation & Icons" from the dropdown menu
Select the library you want and search with keyword
When illustration added, you can change you can change its color and opacity from it's style property panel in the right