How can my student use a image as a background for an HTML website?

Hello I have a student who wants to use an image as a background for his website. How can he make this happen?

I love that your student is wanting to go the extra mile. You can share this link to w3schools with your student if you’d like them to try to figure it out for themselves. I also included a screenshot of the CSS in Web Lab of an easy way to make a background picture. Have fun!

If you’d like it to fit perfectly, use this solution from CSS Tricks:

html { 
  background: url(images/bg.jpg) no-repeat center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;

Thank you so much for your help. My student was able to get this working