一個css控制的特效

=======HTML========

<table width="100%" border="0" cellspacing="1" cellpadding="0">
  <tr>
    <td width="50%" valign="top">
    <div style='height:300;overflow: auto;'>
    <table width="100%" border="0" cellspacing="1" cellpadding="3">
    <thead>
      <tr align="center">
        <th class="TdTitle_Blue">序號</th>
        <th class="TdTitle_Blue">單位名稱</th>
        <th class="TdTitle_Blue">編輯</th>
        <th class="TdTitle_Blue">刪除</th>
      </tr>
      <thead>
      <%
      set conn=opendb("EMSC")
      sql="SELECT * FROM mis_unit"
      set rs=conn.execute(sql)
      if not rs.eof then
        i=1
        while not rs.eof
          if i mod 2 = 1 then
            className = "tdodd"
          else
            className = "tdeven"
          end if
      %>
      <tr>
        <td align="center" class="<%=className%>"><%=i%></td>
        <td  class="<%=className%>"><%=rs("unit")%></td>
        <td align="center"  class="<%=className%>"><img src="Images/icon_edit.gif" alt="編輯" width="19" height="13" onClick="onEdit('<%=rs("unit")%>');" style="cursor:hand;"></td>
        <td align="center"  class="<%=className%>"><img src="Images/icon_delete.gif" alt="刪除" width="15" height="15" onclick="onDelete('mas_unit_delete.asp?unit=<%=rs("unit")%>');" style="cursor:hand;"></td>
      </tr>
      <%
          rs.movenext
          i=i+1
        wend
      else
      %>
      <tr><td colspan="4" align="center">抱歉,暫無資料.</td></tr>
      <%
      end if
      rs.close()
      conn.close()
      %>
    </table>
    </div>
    </td>
    <td width="50%" valign="top"><table width="60%" border="0" align="center" cellpadding="3" cellspacing="0">
      <tr>
        <td colspan="2" class="TdTitle_Blue"><strong>新增/編輯單位</strong></td>
        </tr>
        <form name="frm" method="post" action="mas_unit_save.asp" onsubmit="return Checkinfo();">
      <tr>
        <td><div align="right">單位名稱:</div></td>
        <td><input name="unit" type="text" class="misInput" id="unit"></td>
      </tr>
      <tr>
        <td colspan="2"><div align="center">
          <input name="oldUnit" type="hidden" value="">
          <input name="Submit" type="submit" class="ButtonCom" value="新增">
          &nbsp;
          <input name="Submit2" type="reset" class="ButtonCom" value="重設">
        </div></td>
        </tr>
        </form>
    </table></td>
  </tr>
</table>

====css======

<style>
  thead th, thead th.locked {
    background-color: #6487dc;
    color: #ffffff;
    position:relative;
    cursor: default;}
  thead th {
    top: expression(this.parentElement.parentElement.parentElement.parentElement.scrollTop-2); 
    z-index: 20;}
</style>