수다닷컴

안녕하세요
css로 메뉴를 만들었습니다
그런데 ie7버전에서 z-index가 안먹는것 같네요..
이래저래 수정해보았지만 개선되질 않아요..
뭐가 문제일까요? 고수분들 도와주세요ㅠㅠ
div id=header
h1 class=logoa href=20000/a/h1/a
div class=headerRight
div class=topMenu
div class=gnb
h2 class=hidden글로벌 네비게이션 영역/h2
ul
li class=m1a href=/bbs/content.php?co_id=company0000/a
ul
li style=margin-top:10pxa href=/bbs/content.php?co_id=company인사말/a/li
lia href=/bbs/content.php?co_id=vision비전/a/li
lia href=/bbs/content.php?co_id=history연혁/a/li
lia href=/bbs/content.php?co_id=map찾아오시는 길/a/li
/ul
/li
li class=m2a href=/bbs/content.php?co_id=product제품정보/a
ul
li style=margin-top:10pxa href=/bbs/content.php?co_id=product000/a/li
lia href=/bbs/content.php?co_id=perfect00/a/li
lia href=/bbs/content.php?co_id=frx00/a/li
lia href=/bbs/content.php?co_id=vrx00/a/li
/ul
/li
/ul
/div
/div
/div#header{width:990px; height:71px; z-index:50}
#header .logo a{ display:block; width:300px; height:34px; margin-top:19px;
background:url(images/logo.jpg) 0 0 no-repeat; text-indent: -9999px; float:left;}
#header .headerRight{width:690px; height:71px; float:left;}
#header .topMenu{margin-left:462px; margin-top:10px}
#header .gnb{width:640px; height:85px; margin:auto; margin-top:30px;}
.gnb ullia:hover{color:red;}

/*메인 메뉴 영역 */
.gnbul{width:650px; height:30px; padding:20px 0 0 20px;}
.gnbul.m1{float:left;width:102px;height:30px;margin-right:5px;position:relative;margin-left:72px}
.gnbul.m1a{display:block;width:102px;height:16px;text-align:center;background:url(images/nav_star_off.jpg) 0 0 no-repeat;text-indent:-9999px}
.gnb ul .m1a:hover{background:url(images/nav_star_on.jpg) 0 0 no-repeat;}

.gnbul.m2{float:left;width:75px;height:30px;margin-right:5px;position:relative;margin-left:72px}
.gnbul.m2a{display:block;width:75px;height:16px;text-align:center;background:url(images/nav_product_off.jpg) 0 0 no-repeat;text-indent:-9999px}
.gnb ul .m2a:hover{background:url(images/nav_product_on.jpg) 0 0 no-repeat;} /* 서브메뉴 영역*/
.gnb ul ul{display:none;z-index:50;width:120px;background-color:#dedede}
.gnbulli:hover ul{display:block;width:120px;height:100%;position:absolute;left:0;top:20px}
.gnb li li{width:120px;height:25px;background-color:#dedede}
.gnb li li a{display:block;width:120px;height:100%;background:none;margin-left:10px}
.gnb li li a:hover{display:block;}

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