<li class="my-class">...</li>

#nav li {border-right:1px solid #f00}

and then you have class="no-border" on the last <li> in the list, then you'll need this to remove the border:

#nav li.no-border {border-right:none}

div ul li.no-border a { }

ex)

<?php

$sql = " select *

from {$g5['menu_table']}

where me_mobile_use = '1'

 and length(me_code) = '2'

order by me_order ";

$result = sql_query($sql, false);

$arr_menu_top=array();

$arr_menu_sub=array();

for($i=0; $row=sql_fetch_array($result); $i++) {

$arr_menu_top[]=$row;

$sql2 = " select *

from {$g5['menu_table']}

where me_mobile_use = '1'

 and length(me_code) > '2'

 and substring(me_code, 1, 2) = '{$row['me_code']}'

order by me_order ";

$result2 = sql_query($sql2);

//echo $sql2;

   for ($k=0; $row2=sql_fetch_array($result2); $k++) {

$arr_menu_sub[ $row[me_code] ][]=$row2;

}

}

?>

<style>

ul,ol {list-style:none;}

img {border:none;}

#navi {position:relative; width:100%; height:91px;}

#navi li {float:left; width:33%; background:#60ba2f; text-align:center; padding:15px 0; font-size:10pt; font-family:NanumGothic,'나눔고딕',ng,sans-serif; color:#fff; font-weight:bold; border-right:solid 1px #fff; border-bottom:solid 1px #fff;}

#navi li a {color:#fff;}

#sub_navi {position:relative; width:100%; height:auto; margin-top:30px;}

#sub_navi li {width:100%; background:#8ebf73; text-align:left; padding:10px 0 10px 10px; font-size:10pt; font-family:NanumGothic,'나눔고딕',ng,sans-serif; color:#fff; font-weight:bold; border-right:solid 1px #578a3c; border-bottom:solid 1px #578a3c;}

#sub_navi li a {color:#fff; text-decoration:none;}

#sub_navi li.sub2depth {padding-left:20px;font-weight:normal;}

</style>

<div id="navi">

<ul>

<?

//현재위치 찾기

$cur_me_code='';

foreach($arr_menu_top as $row) {

if (!$cur_me_code && ar_check_menu_url($row['me_link']))

$cur_me_code=$row[me_code];

} 

if (!$cur_me_code) {

foreach($arr_menu_top as $row) {

foreach($arr_menu_sub[ $row[me_code] ] as $row2) { 

if (ar_check_menu_url($row2['me_link'])) {

$cur_me_code=$row[me_code];

break;

}

}

if ($cur_me_code) break;

} 

}

foreach($arr_menu_top as $row) {

?>

<li><a href="<?php echo $row['me_link']; ?>" target="_<?php echo $row['me_target']; ?>"><?=$row['me_name']?></a></li>

<? } ?>

    </ul>

</div>

<? if ($arr_menu_sub[$cur_me_code]) { ?>

<div id="sub_navi">

<ul>

<? foreach($arr_menu_sub[$cur_me_code] as $row) { ?>

<li class='<?=($row[me_order]%100?'sub2depth':'')?>'><a href="<?php echo $row['me_link']; ?>" target="_<?php echo $row['me_target']; ?>"><?=$row['me_name']?></a></li>

<? } ?>

    </ul>

</div>

<? } ?>​