To apply unique styles
Click into the content you want to create specific styles for and click the element pill to open the element menu, where you can create a new class.
Give your custom class a unique name and apply it to the current element. You can now apply styles specifically to this class.
The new custom class will now be listed in the element menu. To apply it to another block of content, simply click into the content, open the element menu and select it. Any style changes will apply to all content marked up to use the custom class.