<div class="bubble"></div>	

html{
	background-color: #222;
	position: relative;
}

.bubble{
    background-image: linear-gradient(#fc0, transparent);
    border-radius: 50%;
    height: 100px;
    left: 10px;
    position: absolute;
    top: 10px;
    width: 100px;
}

.bubble::after{
    background-color: #222;
    border-radius: 50%;
    content: '';
    display: block;
    height: 90px;
    left: 5px;
    position: absolute;
    top: 5px;
    width: 90px;
}