I understand your confusion. From the image name, it is quite hard to find out what the original theme name was that went with it.
An option might be to add the theme name to the image name by replacing
Learn how to create flexible layouts using relative units in CSS. New relative units added in CSS3 include vw(viewports width), vh(viewports height), vmin(minimum of viewports height and width), and vmax (maximum of viewports height and width).