div{
    width: 90%;
    height: 150px;
    border: 2px solid #333;
    margin: 10px auto;
}

#ex1{
    background: radial-gradient(
	yellow, green 10%, purple 20%);
}
#ex2{
    background: repeating-radial-gradient(
	yellow, green 10%, purple 20%);
}
#ex3{
    background: radial-gradient(
	yellow, green 10%, purple 20%, yellow 30%);
}
#ex4{
    background: repeating-radial-gradient(
	yellow, green 10%, purple 20%, yellow 30%);