<!DOCTYPE html>
<html>
    <head>
        <meta charset=utf-8>
        <style type="text/css">
            .topbranch {
                width: 0px;
                height: 0px;
                /*
                * TODO: 上枝叶效果
                */
                float: left;
                margin-left: 100px;
                border-top: 100px solid transparent;
                border-left: 100px solid rgba(0, 0, 0, 0);
                border-right: 100px solid rgba(0, 0, 0, 0);
                border-bottom: 100px solid rgb(0, 128, 0);
            }
            .middleBranch {
                width: 0px;
                height: 0px;
                /*
                * TODO: 中枝叶效果
                */
                border-top: 200px solid rgba(0, 0, 0, 0);
                border-bottom: 200px solid rgb(0, 128, 0);
                border-left:200px solid rgba(0, 0, 0, 0);
                border-right:200px solid rgba(0, 0, 0, 0);
            }
            .base {
                /*
                * TODO: 树干效果
                */
                 float: left;
                 height: 200px;
                 width: 70px;
                 background-color: gray;
                 margin-left: 165px;
            }
        </style>
    </head>
    <body>
    	<section class="topbranch"></section>
        <section class="middleBranch"></section>
        <section class="base"></section>
    </body>
</html>
题目出的不好，可以直接用margin: 0 auto实现居中，不需要浮动