.box-1 {
  background: 
    radial-gradient(lightgreen, darkgreen); 
}

.box-2 {
  background: 
    radial-gradient(ellipse 50px 30px, lightgreen, darkgreen);
}

.box-3 {
  background: 
    radial-gradient(at top left, lightgreen, darkgreen);  
}

.box-4 {
  background: 
    radial-gradient(lightgreen 25%, darkgreen 50%);  
}

.box-1

.box-2

.box-3

.box-4

(CSS3 Gradients at CSS Mine)