<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
.droplet {
width: 4em;
height: 4em;
border-radius: 80% 0 55% 50% / 55% 0 80% 50%;
background-color: #07C;
transform: rotate(-45deg);
}
</style>
</head>
<body>
<div class="droplet"></div>
</body>
</html>
原文：http://www.cnblogs.com/DonaldTrump/p/5773600.html