CSS实现页框问题

   
<div style ="width:538px; height:150px; border:solid 1px gray; padding:10px;">
        <div style =" width:230px; height:150px; float:left; position:relative;">
            <div style ="width:210px; height:44px; position:absolute; left:0; top:0;">
                <img src = "div1.jpg" alt = "" style =" width:45px; height:44px; float:left;" onclick="" onmouseover = "this.src = 'div1_hover.jpg'" onmouseout = "this.src = 'div1.jpg'" />
                <img src = "div4.jpg" alt = "" style =" width:45px; height:44px; float:left;" onclick="" onmouseover = "this.src = 'div4_hover.jpg'" onmouseout = "this.src = 'div4.jpg'" />
                <img src = "div9.jpg" alt = "" style =" width:45px; height:44px; float:left;" onclick="" onmouseover = "this.src = 'div9_hover.jpg'" onmouseout = "this.src = 'div9.jpg'"/>
                <img src = "div16.jpg" alt = "" style =" width:45px; height:44px; f