SOURCE

console 命令行工具 X clear

                    
>
console
<div class="e1"></div>
<div class="e2"></div>
<div class="e3"></div>
div {
  width:15em;
  height:15em;
  margin-bottom:5px;
  background:yellow;
}

.e1 {
  border-radius:50% 50% 0% 0% / 100% 100% 0 0;
}
.e2 {
  border-radius:100% 0 0 100% /50%;
}
.e3 {
  border-radius:100%  0 0;
}