按钮button的css样式（扁平化底色）

        .btn {

            background-image:url("button/btnbg.png");
            border: none;
            color: white;
            font-family:Arial;
            padding: 10px 24px;
            text-align: center;
            text-decoration: none;
            display: inline-block;
            font-size: 18px;
            margin: 4px 2px;
            cursor: pointer;

        }