Datagrid & CSS

[Wasco]

Hi all,
I would like using an extern css file for defining datagrid style:

<asp:datagrid id="DataGrid1" runat="server" GridLines="Horizontal"
CellPadding="3" CssClass="gridDetail">
<AlternatingItemStyle
CssClass="alternate"></AlternatingItemStyle>
<ItemStyle CssClass="itemStyle"></ItemStyle>
<HeaderStyle CssClass="headerStyle"></HeaderStyle>
<PagerStyle HorizontalAlign="Right" Mode="NumericPages"
CssClass="pager"></PagerStyle>
</asp:datagrid>
style.CSS:

..gridDetail{z-index: 101; left: 8px; position: absolute; top: 40px;
height:144px; border-color:#E7E7FF; border-style:none;
border-width:1px; background-color:Red; width:952px;}
..itemStyle{ color:#4A3C8C; background-color:#E7E7FF; font-family:Arial
Narrow;}
..headerStyle{font-weight:bold; color:#F7F7F7;
background-color:#4A3C8C;}
..alternate{background-color:#F7F7F7;}

but doesn't work.
Datagrid doesn't find the styles...

Could you help me?
Thanks