setting attributes or css of button in code behind in aspx

setting attributes or css of button in code behind in aspx

here is my aspx code for buttons
<div id="navigationButtons">
<asp:Button ID="btnSubmit" runat="server" Text="Submit"
OnClick="btnSubmit_Click" CssClass="button submit"
Enabled="true" />
<asp:Button ID="btnNext" name="btnNext" Text="NEXT"
ToolTip="Next" runat="server" CssClass="button next"
TabIndex="0" OnClick="btnNext_Click" Enabled="false"/>
<asp:Button ID="btnPrev" Text="PREV" ToolTip="Previous"
runat="server" CssClass="button prev" TabIndex="2"
OnClick="btnPrev_Click" Enabled="true"/>
<asp:Button ID="btnExit" Text="EXIT" ToolTip="Exit"
runat="server" CssClass="button exit" TabIndex="3"
OnClick="btnExit_Click" />
</div>
I am unable to change the attributes from code behind so I browsed for the
solution and some blogs suggested using following code in the code behind.
((System.Web.UI.HtmlControls.HtmlElement)Page.Form.FindControl("btnNext")).Style.Add("visible",
"false");
but when I use it there is null exception error in the code. I don't know
how to fix this in the above code behind. Any solution is appreciated.
thanks.