*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
.div1{
    background-color: #CCC;
    width: 400px;
    height: 200px; 
    position:absolute;
    top:50%;
    left:50%;
    margin-top: -100px;
    margin-left: -200px;
}
.div2{
    background-color: #FC0;
    width: 50px;
    height: 50px; 
    -webkit-border-radius: 0 0 200px 0;
}
.div3{
    background-color: #FC0;
    width: 50px;
    height: 50px; 
    -webkit-border-radius: 200px 0 0 0;
    position:absolute;
    top:100%;
    left:100%;
    margin-top: -50px;
    margin-left: -50px;
}