word-wrap is not a known CSS property name

i'm trying to wrap a textbox but i'm getting that word-wrap is not a know css property name and it's not working so how can i fix it?

<asp:TemplateField HeaderText="cnt_content">
                <EditItemTemplate>
                    <asp:TextBox ID="cnt_content" runat="server" Text='<%# Bind("cnt_content") %>'  wrap="true" TextMode="MultiLine"></asp:TextBox>
                </EditItemTemplate> 
                <ItemTemplate> 
                    <asp:Label ID="cnt_content" runat="server" Text='<%# Bind("cnt_content") %>'></asp:Label> 
                </ItemTemplate> 
                <ItemStyle Width="800px" wrap="true" />
            </asp:TemplateField> 

note that my textbox is in a gridview and i'm working on asp.net using vb.net

1. Go to options in Visual Studio
2. Select Text-editor
3. Select CSS
4. Select Miscellaneous
5. Under detect errors tick that as warning check box
6. Now your error will become a warning in Visual Studio
7. In browser you will get the result