如何使用css选择器来实现导航栏背景图的切换？

<p class="banner_area">
<p class="item">
<span class="ck_item one" itemType='jjjz'></span>
</p>
<p class="item">
<span class="ck_item two" itemType='jdbg'></span>
</p>
<p class="item">
<span class="ck_item three" itemType='spbj'></span>
</p>
<p class="item  cur_item">
<span class="ck_item four" itemType='ssnz'></span>
</p>
<p class="item ">
<span class="ck_item fiv" itemType='jpnz'></span>
</p>
<p class="item six">
<span class="ck_item six" itemType='hfcz'></span>
</p>
<p class="item" style="margin-right: 0px;">
<span class="ck_item seven" itemType='xbsp'></span>
</p>
</p>

.one{background: url(http://img.jiangcdn.com/home/insider/jujz_one.jpg) no-repeat;}
.two{background: url(http://img.jiangcdn.com/home/insider/jdbg_one.jpg) no-repeat;}
.three{background: url(http://img.jiangcdn.com/home/insider/spbj_one.jpg) no-repeat;}
.four{background: url(http://img.jiangcdn.com/home/insider/ssnz_one.jpg) no-repeat;}
.fiv{background: url(http://img.jiangcdn.com/home/insider/jpnz_one.jpg) no-repeat;}
.six{background: url(http://img.jiangcdn.com/home/insider/hfqz_one.jpg) no-repeat;}
.seven{background: url(http://img.jiangcdn.com/home/insider/xbsp_one.jpg) no-repeat;}
.cur_item{width: 218px;height: 53px;}
.cur_item span.one{background: url(http://img.jiangcdn.com/home/insider/jjjz_two.jpg) no-repeat;}
.cur_item span.two{background: url(http://img.jiangcdn.com/home/insider/jdbg_two.png) no-repeat;}
.cur_item span.three{background: url(http://img.jiangcdn.com/home/insider/spbj_two.jpg) no-repeat;}
.cur_item span.four{background: url(http://img.jiangcdn.com/home/insider/ssnz_two.jpg) no-repeat;}
.cur_item span.fiv{background: url(http://img.jiangcdn.com/home/insider/jpnz_two.jpg) no-repeat;}
.cur_item span.six{background: url(http://img.jiangcdn.com/home/insider/hfqz_two.jpg) no-repeat;}
.cur_item span.seven{background: url(http://img.jiangcdn.com/home/insider/xbsp_two.jpg) no-repeat;}