h1 {
  background-image: url(hello.png?v=0.2.0);
}

h2 {
  background-image: url('//cdn.1.test.com/hello.png');
}

h3 {
  background-image: url("//cdn.2.test.com/hello.png");
}

h4 {
  background-image: url(data:image/png;base64,TEST==);
}

h5 {
  background-image: url('data:image/png;base64,TEST==');
}