鼠标悬停，背景颜色变化问题

实例代码：
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <style type="text/css">
        *{margin: 0; padding: 0;}
        .container{
            margin: 0 auto;
            padding-top: 30px;
            width: 1000px;
        }
        .btn{
            display: inline-block;
            padding: 0 30px;
            width: auto;
            height: 35px;
            font: 14px/35px 'microsoft yahei';
            color: #fff; border: 0;
            border-radius: 3px;
            text-align: center;
            cursor: pointer;
            /*实现渐变（时间变化效果）*/
            -webkit-transition: all .5s;
            -moz-transition: all .5s;
            -ms-transition: all .5s;
            -o-transition: all .5s;
            transition: all .5s;
        }
        .blueBtn{
            background: #5dcbff;
        } /*蓝色按钮*/
        .blueBtn:hover{
            background: #40b6ee;
        }
        .orangeBtn{
            background: #ff5700;
        }/*橙色按钮*/
        .orangeBtn:hover{
            background: #e25d18;
        }
        .violetBtn{
            background: #6680ff;
        }/*紫色按钮*/
        .violetBtn:hover{
            background: #425de0;
        }
        .grayBtn{
            background: #999;
        }/*灰色按钮*/
        .grayBtn:hover{
            background: #7f7f7f;
        }
    </style>
</head>
<body>
<div class="container">
    <span class="btn blueBtn">蓝色按钮</span>
    <span class="btn orangeBtn">橙色按钮</span>
    <span class="btn violetBtn">紫色按钮</span>
    <span class="btn grayBtn">灰色按钮</span>
</div>
</body>
</html>
同理可应用在超链接、按钮等中