Just change the custom property values on the <chat-ui> node. For a list of what you can change, find it here. Or, don't use custom properties, and update the NextCSS config to compile the variables, then you can do it a more SCSSy way, and support more browsers. This is the primary component that you should be dealing with. It has the easy API, for quick access to the most common tasks in a chat widget. You shouldn't need the API's for the other components, but you can leverage them if you want to.