A Theme Builder project lets you define a set of common CSS properties and tokens for Lightning and Avonni components. Your Style Library will be applied by default on your lightning web components. It will help create a consistent look and feel for your work.
Once you have created and published a Style Library, all the UI elements that are part of the CSS style rule will inherit our custom CSS settings and tokens
As an example, let’s say we received the color palette information from our design team. To create a consistent look that matches our company branding theme and colors , creating a Style Library rule using Avonni Builder will definitely help us.
View all the differences between Avonni Designer and Avonni Builder.