In Chrome (any other browser with developer tools would be able to do this as well) I just right clicked on the animation area and clicked "Inspect Element". Doing that exposes the developer tools which includes the ability to make live edits to CSS. The animation window is, very nicely, contained in a single element "p#fluid". From the developer tools it's a simple matter to change the color declaration from red to green and add a new "background-color: black" property.