CSS Integration for Controls in ASP .Net

Hi All,
I have developed webform with some controls..
When i was developing that automaticall some Inline styles were created simultaneously..

Now i need to applicable CSS for that controls..
But its not showing in output..

Previous Code:

<

td class="style12"><asp:DropDownList ID="ddSIREmp" runat="server" Height="27px" style="margin-bottom: 0px" Width="104px" TabIndex="2">
asp:DropDownList>


Revised Code:

 <td>
<asp:DropDownList ID="ddSIREmp" runat="server" style="margin-bottom: 0px" TabIndex="2" cssclass="dlist">
asp:DropDownList>


my CSS class as follows

App.css

.ddList

{

font-family:Arial;

height:25;

width:100;

}

After applying css class to my control its not showing the control with revised effects..

How can i do this...