js里InnerHTMl如何加入样式

本来样式是这样的<div id="time"><span class="time">10</span><span>小时</span><span class="time">20</span><span>分</span><span class="time">30</span><span>秒</span></div>
JS是这样的
var Now=new Date();    
var EndTime=new Date(Now .getFullYear() ,Now .getMonth() ,Now .getDate() ,Now.getHours()+0 ,Now.getMinutes()+120 ,Now.getSeconds() );
function Time()
{   
    var timeold=(EndTime.getTime()-new Date ().getTime());
    var sectimeold=timeold/1000
    var secondsold=Math.floor(sectimeold);
    var msPerDay=24*60*60*1000
    var e_daysold=timeold/msPerDay
    var daysold=Math.floor(e_daysold);
    var e_hrsold=(e_daysold-daysold)*24;
    var hrsold=Math.floor(e_hrsold);
    var e_minsold=(e_hrsold-hrsold)*60;
    var minsold=Math.floor((e_hrsold-hrsold)*60);
    var seconds=Math.floor((e_minsold-minsold)*60);
    document.getElementById ("Time").innerHTML = "<span class='timer'>"+hrsold+"</span>"+"小时"+minsold+"分"+seconds+"秒";
    setTimeout ("Time();",1000);
 }我现在在document.getElementById ("Time").innerHTML = "<span class='timer'>"+hrsold+"</span>"+"小时"+minsold+"分"+seconds+"秒";里加入样式, 但样式不起作用了, 请问该怎么加了