CSS dropdown menu

HI All,

I have problem with css dropdwon menu, when hover the tab how can i remove black like

See attached image

Here is my css and HTML code

<!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>Untitled Document</title>
<style type=“text/css”>
<!–
body {
margin-left: 0px;
margin-top: 0px;
margin-right: 0px;
margin-bottom: 0px; font-family:Arial, Helvetica, sans-serif; font-size:12px;
}
.g-nav{ margin:0 auto; height:45px; background:#ccc; padding-left:15%;}
.nav{ float:left; list-style-type:none; line-height:43px; position:relative; padding:0 15px; z-index:99; border-color:#ccc #ccc #ccc #ccc; border-style:solid; border-width:1px;}
.nav a{ color:#000; text-decoration:none; font-weight:bold; font-size:14px; display:block; }
.nav a:hover{ background:; color:#000; padding-bottom:1px;}
.nav:hover{ background:#f9f9f9; color:#000; padding-bottom:2px; border-color:#000 #000 #fff #000; border-style:solid; border-width:1px; }
.nav:hover a{ color:#000;}
.nav:hover ul{display:block;}
/submenu/
.nav ul{
position:absolute;
display:none;
width:200px;
left:-1px;
top:44px;
background:#f9f9f9;
border:1px solid #000;
padding:0px;
margin:0px;
z-index:-99;
}
.nav ul li{ list-style-type:none; line-height:normal;}
.nav ul li a{ color:#000; padding:10px;}
.nav ul li a:hover{ background:#000;}
–>
</style></head>

<body>
<ul class=“g-nav”>
<li class=“nav sele”><a href="#" >Home</a>
<ul style=“display:;”>
<li><a href="#">Current researchers, students & staff</a></li>
<li><a href="#">Our areas of strength</a></li>
<li><a href="#">Institutes and centres</a></li>
<li><a href="#">Partnership and consultancy</a></li>
<li><a href="#">Office of Research and Development</a></li>
</ul>
</li>
<li class=“nav”><a href="#">About Us</a><ul>
<li><a href="#">Current researchers, students & staff</a></li>
<li><a href="#">Our areas of strength</a></li>
<li><a href="#">Institutes and centres</a></li>
<li><a href="#">Partnership and consultancy</a></li>
<li><a href="#">Office of Research and Development</a></li>
</ul></li>
<li class=“nav”><a href="#">Services</a><ul>
<li><a href="#">Current researchers, students & staff</a></li>
<li><a href="#">Our areas of strength</a></li>
<li><a href="#">Institutes and centres</a></li>
<li><a href="#">Partnership and consultancy</a></li>
<li><a href="#">Office of Research and Development</a></li>
</ul></li>

<li class=“nav”><a href="#">Products</a><ul>
<li><a href="#">Current researchers, students & staff</a></li>
<li><a href="#">Our areas of strength</a></li>
<li><a href="#">Institutes and centres</a></li>
<li><a href="#">Partnership and consultancy</a></li>
<li><a href="#">Office of Research and Development</a></li>
</ul></li>

<li class=“nav”><a href="#">Home</a><ul>
<li><a href="#">Current researchers, students & staff</a></li>
<li><a href="#">Our areas of strength</a></li>
<li><a href="#">Institutes and centres</a></li>
<li><a href="#">Partnership and consultancy</a></li>
<li><a href="#">Office of Research and Development</a></li>
</ul></li>

<li class=“nav”><a href="#">Home</a><ul>
<li><a href="#">Current researchers, students & staff</a></li>
<li><a href="#">Our areas of strength</a></li>
<li><a href="#">Institutes and centres</a></li>
<li><a href="#">Partnership and consultancy</a></li>
<li><a href="#">Office of Research and Development</a></li>
</ul></li>

</ul>
</body>
</html>

Thank you
Sidd