箭头显示有部分问题
只有二级菜单的第一个li和三级菜单第一个li有箭头，且三级菜单的箭头经过时还有问题，用的谷歌浏览器，求解
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>css3下拉菜单</title>
<style type="text/css">
*{
margin:0;
padding:0;
}
li{
list-style:none;
}
a{
text-decoration:none;
}
.top_nav{
width:960px;
margin:60px auto;
border:1px solid #222;
background-color:#111;
background-image:linear-gradient(#444,#111);
border-radius:6px;
box-shadow:0px 1px 1px #777;
}
.top_nav:before,.top_nav:after{
content:" ";
display:table;
}
.top_nav:after{
clear:both;
}
.top_nav{
zoom:1;/*zoom<IE8*/
}
.top_nav li{
float:left;
border-right:1px solid #222;
box-shadow:1px 0 0 #444;
text-align:center;
position:relative;
}
.top_nav li a{
float:left;
padding:12px 30px;
color:#999;
font:bold 12px;
display:block;
text-shadow:0px 1px 0px #000;
}
.top_nav li a:hover{
color:#fafafa;
}
.top_nav li ul{
visibility:hidden;
position:absolute;
top:38px;
left:0;
z-index:1;
background-color:#444;
background-image:linear-gradient(#444,#111);
box-shadow:0 -1 0 rgba(255,255,255,.3);
border-radius:3px;
opacity:0;
margin:20px 0 0 0;
transition:all .2s ease-in-out;
}
.top_nav li:hover > ul{
opacity:1;
visibility:visible;
margin:0;
}
.top_nav ul li{
float:none;
border:0;
display:block;
box-shadow:0 1px #111,0 2px #666;
}
.top_nav ul li:last-child{
box-shadow:0 1px transparent,0 2px transparent;
}
.top_nav ul a{
padding:10px;
width:130px;
display:block;
float:none;
}
.top_nav ul a:hover{
background-color:#0186ba;
background-image:linear-gradient(#04acec,#0186ba);
}
.top_nav ul li:first-child > a{
border-radius:3px 3px 0 0;
}
.top_nav ul li:last-child > a{
border-radius:0 0 3px 3px;
}
.top_nav ul li:first-child > a:before{
content:" ";
position:absolute;
left:40px;
top:-6px;
border-bottom:6px solid #444;
border-left:6px solid transparent;
border-right:6px solid transparent;
}
.top_nav ul li:first-child >a:hover:before{
border-bottom-color:#04acec;
}
.top_nav ul ul{
top:0;
left:150px;
margin:0 0 0 20px;
box-shadow:-1px 0 0 rgba(255,255,255,.3);
}
.top_nav ul ul li:first-child a:before{
top:50%;
left:-6px;
margin-top:-6px;
border-left:0;
border-top:6px solid transparent;
border-bottom:6px solid transparent;
border-right:6px solid #3b3b3b;
}
.top_nav ul ul li:first-child a:hover:bofore{
border-right-color:#0299d3;
border-bottom-color:transparent;
}
</style>
</head>
<body>
<ul class="top_nav">
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</ul>
</li>
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<li><a href="#">后台编程</a></li>
</ul>
</li>
<li><a href="#">关于我们</a></li>
</ul>
</body>
</html>
