body{
  background: black;
}
h1{
 color:white;
  text-align:center;
  font-size:40pt;
}
#red-box{
  background: radial-gradient(red,white,red); 
}
#orange-box{
  background: radial-gradient(orange,white,orange); 
}
#yellow-box{
  background: radial-gradient(yellow,white,yellow);  
}
#green-box{
  background: radial-gradient(green,white,green); 
}
#blue-box{
  background: radial-gradient(blue,white,blue);  
}
#violet-box{
  background: radial-gradient(violet,white,violet); 
}
#rainbow-box{
  background: 
    radial-gradient(red,orange,yellow,green,blue,violet,white,white);
}
#black-white-box{
  background: radial-gradient(black,white,black,white,black);
}
#container  div{
    height:400px;
    width:400px;
    border-radius:50%;
    margin: auto;
    margin-bottom: 20px;
  }