Can anyone help me out in understanding RGB model to apply on code I.e hexa decimals

Tell us what’s happening:

Your code so far

  body {
    background-color: black;

Your browser information:

Your Browser User Agent is: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36.

Link to the challenge:

What is your question? The challenge tells you exactly what to do. There really is nothing to figure out to solve the challenge. Most of the challenge information is educational. The last paragraph tells you how to pass the challenge.