Border radius 1

HTML

border-radius: 20px 30px 
<div id="cas1"></div>
border-radius: 20px 30px 40px
<div id="cas2"></div>
border-radius: 20px 30px 40px 50px
<div id="cas3"></div>

CSS

div {
    margin: 10px;
    border: 2px solid blue;
    padding: 10px; 
    background: blue;
    width: 100px;
    height: 50px;
}
#cas1 {
    border-radius: 20px 30px;
}
#cas2 {
    border-radius: 20px 30px 40px;
}
#cas3 {
    border-radius: 20px 30px 40px 50px;
}