Applying css to textbox for compulsary feild

Applying css to textbox for compulsary feild

1)
2)
I have a textbox which looks like 1st image. Instead of giving '*' mark
for compulsory fields to be filled I want to depict the text box's right
bottom corner marked with RED color. I am able to format as shown in image
1. I wan the output something like the 2nd image where the red color is in
right angle to the right-bottom. Foloowing is my css that I am using.
lease help how I can achieve format like 2nd image.
Css:
.txtbxcomp
{
width: 120px;
height: 25px;
background-color: #F9F9F9;
border: 1px solid #CCCCCC;
text-transform:uppercase;
font-family: Calibri;
font-size: 14px;
/*border-bottom-right-radius:1px;
border-top-color:red;*/
border-right-width:1px;
border-right-color:red;
border-bottom-width:1px;
border-bottom-color:red;
}
And my text box is
<td class="r1" width="15%">PO No:
</td>
<td width="18%">
<asp:TextBox ID="txt_Po_No"
runat="server" Height="95%"
CssClass="txtbxcomp"
></asp:TextBox>
<%--<span style="color:
Red;">*</span>--%>
</td>