This example uses CartoDB.js to display an interactive map inside a full-screen div. The code initializes a map with a single custom overlay button labeled “Do Something,” which sits in the top-right corner and changes its background on hover. The map itself is rendered using the CartoDB library’s tile layers, while the button is styled with the included cartodb-infobox CSS class. The JavaScript structure defines a main function tied to the window load event, though no map layers or data sources are explicitly loaded in the provided snippet.