svg图片当button
svg图片是文本定义的。可以去icomoon等svg网站下载，
下载好了有两种使用方式，
1 直接在html中声明svg是什么
<html>
<head>
<svg aria-hidden="true" style="position: absolute; width: 0; height: 0; overflow: hidden;" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<defs>
<symbol id="icon-enlarge2" viewBox="0 0 32 32">
<path d="M32 0v13l-5-5-6 6-3-3 6-6-5-5zM14 21l-6 6 5 5h-13v-13l5 5 6-6z"></path>
</symbol>
<symbol id="icon-shrink2" viewBox="0 0 32 32">
<path d="M14 18v13l-5-5-6 6-3-3 6-6-5-5zM32 3l-6 6 5 5h-13v-13l5 5 6-6z"></path>
</symbol>
<symbol id="icon-list2" viewBox="0 0 32 32">
<path d="M12 2h20v4h-20v-4zM12 14h20v4h-20v-4zM12 26h20v4h-20v-4zM0 4c0-2.209 1.791-4 4-4s4 1.791 4 4c0 2.209-1.791 4-4 4s-4-1.791-4-4zM0 16c0-2.209 1.791-4 4-4s4 1.791 4 4c0 2.209-1.791 4-4 4s-4-1.791-4-4zM0 28c0-2.209 1.791-4 4-4s4 1.791 4 4c0 2.209-1.791 4-4 4s-4-1.791-4-4z"></path>
</symbol>
</defs>
</svg>
<style>
#toc {
font-size: 16px; width: 10em; height: 10em;}
</style>
</head>
<body>
<div id="toc"> <svg class="icon icon-enlarge2"><use xlink:href="#icon-enlarge2"></use></svg><span class="name"> icon-enlarge2</span></div>
</body>
</html>
2 像使用图片一样用url的形式使用svg文件。好处是html能小一些。
<html>
<head>
<style>
#toc {
background-image: url("enlarge2.svg");
background-size: cover;
background-repeat: no-repeat;
font-size: 16px; width: 10em; height: 10em;}
</style>
</head>
<body>
<div id="toc"> </div>
</body>
</html>