<style>
.box{
width: 400px;
height: 400px;
margin: 100px auto;
transition: 5s linear;
}
.box div{
width: 180px;
height: 180px;
margin: 10px;
border: 1px solid #000;
box-sizing: border-box;
float: left;
background: #f00;
}
.box div:nth-of-type(1),.box div:nth-of-type(4){
border-radius: 0 70%;
}
.box div:nth-of-type(2),.box div:nth-of-type(3){
border-radius: 70% 0;
}
.box:hover{
transform: rotate(720deg);
}
</style>
<div class="box">
<div></div>
<div></div>
<div></div>
<div></div>
</div>