Navicon Transformicons: Animated Navigation Icons with CSS Transforms
http://sarasoueidan.com/blog/navicon-transformicons/
CSS3 box-shadow
http://www.w3cplus.com/content/css3-box-shadow
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="utf-8">
<title></title>
<style>
button {display: inline-block;margin: 0 1em;border: none;background: none;background: #000;}
button span {display: block;}
.grid-button {padding: 2rem;cursor: pointer;user-select: none;}
.grid-button .grid {width: 1rem;height: 1rem;background: #ecf0f1;color: #ecf0f1;transition: 0.3s;}
.grid-button.collapse .grid {box-shadow: -1.25rem 0, -1.25rem 1.25rem, 1.25rem 0, 1.25rem -1.25rem, 0 -1.25rem, -1.25rem -1.25rem, 0 1.25rem, 1.25rem 1.25rem;}
</style>
</head>
<body>
<button type="button" role="button" aria-label="Toggle Navigation" class="grid-button collapse">
<span class="grid"></span>
</button>
</body>
</html>