When a user clicks a spot with overlapping features, the pop-up panel that is triggered displays on the right-corner a 'feature-menu-button' and R/L arrows, indicating how many features overlap and prompting the user to click through to view their details.
I am using Experience Builder Developer 1.12.
I want to change the background-color of the 'esri-popup__feature-menu-button' to cyan to draw the user's eye to ensure overlapping features aren't overlooked. I think I can do this by creating a custom theme and adding a style.ts as described in this Sample Code, but I don't know where to find and identify the elements. Where do I begin?
Thanks so much in advance!

The demo screenshot was made to the HTML page by adding
