单选按钮组选中的按钮默认样式替换成图片

 要实现下面单选按钮组的选中状态用图片显示： 

html结构：

　　　　　　　　　　　　　　<div class="select-radio-box">
                            <div class="select-box">
                                <input value="0" type="radio" name="sex" id="male" checked="checked">
                                    <label for="male">男士</label>
                            </div>
                            <div class="select-box">
                                <input value="1" type="radio" name="sex"  id="female">
                                    <label for="female">女士</label>
                            </div>
                                <div class="select-box">
                                <input value="2" type="radio" name="sex"  id="secrecy">
                                    <label for="secrecy">保密</label>
                            </div>
                        </div>

样式： 

/*单选按钮 Begin*/
.select-radio-box {
    display: inline-block;
}
.select-box {
    display: inline-block;
    margin-right: 78px;
    box-sizing: border-box;
    padding-left: 42px;
    position: relative;
}
.select-box input {
    width: 0;
    height: 0;
    margin-right: 12px;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 0;
}
 /*input 选中前的样式*/
.select-box input[type="radio"] + label:before {
    content: "a0";  /*不换行空格*/
    display: inline-block;
    width: 20px;
    height: 20px;
    background-color: #ffffff;
    border-radius: 2px;
    border: solid 1px #dddddd;
    vertical-align: middle;
    margin-right: 12px;
    position: absolute;
    top: 32px;
    left: 0;
    behavior:url("/jrcz/js/pie_file/PIE.htc");
 }
 /*input 选中后的样式 */
 .select-box input[type="radio"]:checked + label:before {
    border: solid 1px #2266cb;
    background:#2266cb url(../images/icons/get_icon.png) no-repeat center center;/*背景图的写法是生效的*/
 }