How to give a div oval shape?

Question

I tried a lot on oval shape which have cut in both sides but not able to do it please <

Answer 1

Change the values on css:

#demo {
    width: 100%;
    height: 600px;
    background: white;
    -moz-border-radius: 50% / 250px;
    -webkit-border-radius: 40% / 250px;
    border-radius: 50% / 250px;

    z-index: 100;
    position: relative;
}