You could use an asymmetrical border to make curves with CSS.
border-radius: 50%/100px 100px 0 0;
.box {_x000D_
width: 500px; _x000D_
height: 100px; _x000D_
border: solid 5px #000;_x000D_
border-color: #000 transparent transparent transparent;_x000D_
border-radius: 50%/100px 100px 0 0;_x000D_
}
_x000D_
<div class="box"></div>
_x000D_