Does your example not work in CodePen? The CodePen environment is a little different than the web page environment that contain the CodePen. Sometimes, when you follow the instructions to add the ...

How to Add an Image to a CSS File. Web pages normally add images using the inline HTML "img" tag. CSS coding usually doesn't set an image's source because CSS controls design rather than content.

Some example pages have more than one example or specific language, so the information passed to sourceCode.add specifies where in the page to find the example html, the javascript and css file links ...