We can use css3 radial-gradient() as well to draw this shape:
.halfOval {
background: radial-gradient(ellipse at 50% 100%, #a0C580 70%, transparent 70%);
}
.halfOval {
background: radial-gradient(ellipse at 50% 100%, #a0C580 70%, transparent 70%);
margin: 50px auto;
height: 100px;
width: 400px;
}