What's the difference between background and background-color in css?

I did I use background in css and the challenge told me to use background-color.
background looked exactly the same as background-color, so can you please tell me the difference between them?

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36.

Link to the challenge: