Reference file in public folder from CSS in create-react-app

Just use a / before the name, this will make it relative to the output root, which includes anything in the public folder (provided the finished hosted application is served at the root of a domain).

so for the question asked above:

.App-header {
  background-color: #222;
  height: 150px;
  padding: 20px;
  color: white;
  background-image: url("/example.png");
}

the critical part being

/example.png 

refers to a file, example.png, that is in the public folder (served at the root level)

Could also be relative:

one could also use

./example.png

provided that the css file was also imported from the public/build directory, this would be relative to the css file and not depend on being served at the domain root, but typically in CRA webpack will bundle the CSS and it may or may not be loaded from this location. (you could import it in the html file directly using rel tag with the %PUBLIC_URL%/Styles.css macro)