Hi Heidi!
Great question! You can create this using variables that change the states of the buttons on the initial slide. I've created a sample project for you that includes these variables.
In the project, click on the button "Slide One" and continue navigating through the lightboxes using the Next button. Close the lightbox at any time, and when returning the first slide, there should be buttons in the visited state that correspond with the slides already viewed.
Please take a look and let me know if you have additional questions!
