Css-a:hover discoloration Problem

Today in helping our school to do the website, because in the CSS here is not very good, the process found a problem, a:hover, the color of the font will not change. Later only to discover the problem of nesting a and Div,

My CSS code is:

. Left_box. Lb_wrap. Lb_theme{Color:#900;text-align:Center;Height:30px;Display:Block;; Margin-left:Auto;Margin-top:1px;Line-height:35px;}. Left_box. Lb_wrap a{Display:Block;text-align:Center;Height:30px;width:100%;}. Left_box. Lb_wrap a:link{Color:#900;background:#FFF no-repeat 5px 12px;text-decoration:None;}. Left_box. lb_wrap a:hover{Color:#FFF;/*when the mouse is over, the font should change to that hue (white), but it doesn't actually*/background:#800 no-repeat 5px 12px;font-size:12px;Font-weight:Bolder;text-decoration:None;}. Left_box{Border:1px solid #09F;Margin-top:16px;}/*lb:left Box*/. Left_box. Lb_wrap{width:95%;background:#900;Margin-top:5px;Margin-left:Auto;Margin-bottom:30px;Font:Arial, "The song Body";}

The HTML code is:

<Divclass= "Left_box"><Divclass= "Lb_wrap">    <Divclass= "Lb_title">National and Guangxi characteristic specialty</Div>    <ahref= "/item/88951.aspx">    <Divclass= "Lb_theme">Geographic Information System</Div> <!--div cannot be placed in a DIV, otherwise a:hover does not work--    </a>    <Divclass= "Lb_theme"><ahref= "/item/88943.aspx">Geography Science (Teacher education)</a></Div></Div>

Css-a:hover discoloration Problem