How can I customise my Overlay?

Variables are used to control what is displayed within your components on your overlay. The full list of available variables can be found at Variables List. Open the settings panel (F3) and paste your amended variables into Initial Variable Values.
CSS Style Overrides are used to change how your components look (size, shape, position, color, font, images, animations etc…) in the overlay. Check out Editing CSS Styles for instructions on getting started using your own code.