Page Themes and Skins Change in ASP.NET

Step 1: Take Asp.net web Form and Dropdownlist

Step 2: First you have to add an App_Themes folder for adding skins, css and images.

Such as in the following example, you can take any Skin to be used in an Application:

<asp:Label runat="server" ForeColor="#000066" BackColor="transparent"></asp:Label>

<asp:TextBox runat="server" ForeColor="#000066" BorderWidth="1px" BorderStyle="Solid" BorderColor="#000066" BackColor="Transparent"></asp:TextBox>

<asp:Button runat="server" BorderStyle="Solid" BorderColor="#000066" BorderWidth="1pt" ForeColor="#000066" BackColor="#EEEEEE"></asp:Button>

<asp:HyperLink runat="server" Font-Underline="True" BorderStyle="None" Backc></asp:HyperLink>

<asp:WebPartZone runat="server" BackColor="#E6E6FA" DragHighlightColor="#0000FF" ShowIconInPartTitle="True" BorderStyle="Solid" BorderWidth="2pt" BorderColor="#000066">

<FooterStyle BackColor="#CCCCCC"></FooterStyle>
<HelpVerb imageurl="images/basicblue_help.gif"></HelpVerb>
<PartStyle ForeColor="#000000" BorderColor="#000066" BackColor="#FFFFFF"></PartStyle>
<PartTitleStyle ForeColor="#FFFFFF" BorderColor="#000066" BackColor="#000066"></PartTitleStyle>
<VerbStyle ForeColor="Navy" BackColor="#EEEEEE" BorderWidth="1px" BorderStyle="solid" BorderColor="Navy"></VerbStyle>
<CloseVerb imageurl="images/basicblue_close.gif"></CloseVerb>
<RestoreVerb imageurl="images/basicblue_restore.gif"></RestoreVerb>
<MinimizeVerb imageurl="images/basicblue_minimize.gif"></MinimizeVerb>
<EditVerb imageurl="images/basicblue_edit.gif"></EditVerb>
</asp:WebPartZone>

<asp:CatalogZone runat="server" DragHighlightColor="#0000FF" ShowIconInPartTitle="True" BorderStyle="solid" BorderColor="#000066" BorderWidth="2pt" BackColor="#E6E6FA">
<FooterStyle BackColor="#EEEEEE"></FooterStyle>
<PartStyle ForeColor="#FFFFFF" BorderColor="#000066" BackColor="#EEEEEE"></PartStyle>
<PartTitleStyle ForeColor="#FFFFFF" BorderColor="#000066" BackColor="#000066"></PartTitleStyle>
<VerbStyle ForeColor="#000066" BackColor="#EEEEEE" BorderColor="#000066" BorderStyle="solid" BorderWidth="1"></VerbStyle>
</asp:CatalogZone>

<asp:EditorZone runat="server" DragHighlightColor="#0000FF" ShowIconInPartTitle="True" BorderStyle="solid" BorderColor="#000066" BorderWidth="2pt" BackColor="#E6E6FA">
<FooterStyle BackColor="#EEEEEE"></FooterStyle>
<PartStyle ForeColor="#FFFFFF" BorderColor="#000066" BackColor="#FFFFFF"></PartStyle>
<PartTitleStyle ForeColor="#FFFFFF" BorderColor="#000066" BackColor="#000066"></PartTitleStyle>
<VerbStyle ForeColor="#000066" BorderColor="#000066" BackColor="red"></VerbStyle>
</asp:EditorZone>

<asp:Calendar runat="server" BorderWidth="2px" BorderColor="#CCCCCC" BackColor="#EEEEEE">
<TodayDayStyle BackColor="#CCCCCC" Forecolor="#0000DD"></TodayDayStyle>
<SelectedDayStyle ForeColor="#0000FF" BorderColor="#000066" BackColor="#FFFFFF"></SelectedDayStyle>
<TitleStyle Font-Bold="True" ForeColor="#FFFFFF" BackColor="#000066"></TitleStyle>
<DayHeaderStyle Font-Bold="True" ForeColor="#000066" BackColor="#EEEEEE"></DayHeaderStyle>
<NextPrevStyle ForeColor="#FFFFFF" BackColor="#000066"></NextPrevStyle>
<OtherMonthDayStyle BackColor="#EEEEEE" ForeColor="#AAAAAA"></OtherMonthDayStyle>
<DayStyle ForeColor="#000000" BackColor="#EEEEEE"></DayStyle>
<WeekEndDayStyle BackColor="#EEEEEE" ForeColor="#000000"></WeekEndDayStyle>
</asp:Calendar>

<asp:DataGrid runat="server" BackColor="#CCCCCC" BorderWidth="2pt" BorderStyle="Solid" BorderColor="#CCCCCC" GridLines="None" HorizontalAlign="Left">
<PagerStyle ForeColor="#FFFFFF" BackColor="#CCCCCC"></PagerStyle>
<AlternatingItemStyle BackColor="#EEEEEE" ForeColor="#000000"></AlternatingItemStyle>
<EditItemStyle ForeColor="#FFFFFF" BackColor="#FFFFE0" BorderColor="#FFFFFF"></EditItemStyle>
<FooterStyle ForeColor="#FFFFFF" BackColor="#AAAAAA"></FooterStyle>
<ItemStyle ForeColor="#000000" BackColor="#FFFFFF"></ItemStyle>
<HeaderStyle ForeColor="#FFFFFF" BackColor="#000066"></HeaderStyle>
<SelectedItemStyle BorderColor="#CCCCCC" BackColor="#FFFFE0" ForeColor="#000000"></SelectedItemStyle>
</asp:DataGrid>

<asp:GridView runat="server" BackColor="#CCCCCC" BorderWidth="1pt" BorderColor="#CCCCCC" GridLines="None" HorizontalAlign="Left">
<FooterStyle ForeColor="#FFFFFF" BackColor="#AAAAAA"></FooterStyle>
<EditRowStyle BorderWidth="1pt" ForeColor="#000000" BorderStyle="Solid" BorderColor="#0000FF" BackColor="#FFFFE0"></EditRowStyle>
<HeaderStyle Font-Bold="True" ForeColor="#FFFFFF" BackColor="#000066"></HeaderStyle>
<AlternatingRowStyle BorderWidth="2pt" ForeColor="#000000" BorderStyle="Solid" BorderColor="#CCCCCC" BackColor="#EEEEEE"></AlternatingRowStyle>
<SelectedRowStyle ForeColor="#000000" BorderColor="#0000EE" BorderWidth="2" BackColor="#FFFFE0"></SelectedRowStyle>
<RowStyle BackColor="#FFFFFF" ForeColor="#000000"></RowStyle>
<PagerStyle BorderWidth="1pt" Font-Bold="True" Font-Size="1.2em" BorderColor="#0000FF" BorderStyle="Solid" ForeColor="#000000" BackColor="#AAAAAA"></PagerStyle>
</asp:GridView>

<asp:DataList runat="server" BorderStyle="Solid" BorderColor="#CCCCCC" BackColor="#CCCCCC">
<AlternatingItemStyle BackColor="#EEEEEE" BorderColor="#EEEEEE"></AlternatingItemStyle>
<EditItemStyle ForeColor="#000066" BackColor="#FFFFE0" BorderColor="#000066" BorderStyle="solid" BorderWidth="1pt"></EditItemStyle>
<FooterStyle Font-Bold="True" ForeColor="#000066" BackColor="#FFFFFF" BorderColor="#EEEEEE"></FooterStyle>
<ItemStyle BackColor="#FFFFFF" BorderColor="#EEEEEE"></ItemStyle>
<HeaderStyle Font-Bold="True" BorderColor="#000066" BorderStyle="solid" ForeColor="#FFFFFF" BackColor="#000066"></HeaderStyle>
<SelectedItemStyle ForeColor="#000066" BackColor="#E6E6FA" BorderColor="transparent" BorderWidth="1pt"></SelectedItemStyle>
</asp:DataList>

<asp:DetailsView runat="server" ForeColor="#000000" BorderWidth="2pt" BorderStyle="Solid" BorderColor="#CCCCCC" BackColor="#EEEEEE" CellPadding="5">
<HeaderStyle BackColor="#000066" BorderColor="#EEEEEE"></HeaderStyle>
<PagerStyle ForeColor="#000066" BackColor="#EEEEEE"></PagerStyle>
<EditRowStyle BorderColor="#000066" BackColor="#FFFFFF" ForeColor="#000000"></EditRowStyle><RowStyle BackColor="#FFFFFF" BorderColor="#000066"></RowStyle>
<CommandRowStyle Font-Bold="True" ForeColor="#000066" BackColor="#CCCCCC" BorderColor="#000066"></CommandRowStyle>
<InsertRowStyle BackColor="#FFFFFF" BorderColor="#EEEEEE"></InsertRowStyle>
<FooterStyle BackColor="#EEEEEE" ForeColor="#000000" BorderColor="#EEEEEE"></FooterStyle>
<AlternatingRowStyle BackColor="#EEEEEE" BorderColor="#EEEEEE"></AlternatingRowStyle>
</asp:DetailsView>

<asp:TreeView runat="server" ForeColor="#000066" BackColor="transparent" BorderColor="#EEEEEE" ParentNodeImageUrl="images/basicblue_greysquare.gif" RootNodeImageUrl="images/basicblue_greysquare.gif" NodeIndent="10" LeafNodeImageUrl="images/basicblue_greysquare.gif">
<NodeStyle horizontalpadding="5" ForeColor="#000066" verticalpadding="1" BackColor="#FFFFFF"></NodeStyle>
<LeafNodeStyle ForeColor="#000066" BackColor="#FFFFFF"></LeafNodeStyle>
<LevelStyles>
<asp:TreeNodeStyle Font-Bold="True" BackColor="#FFFFFF" ForeColor="#000066" ChildNodesPadding="5"></asp:TreeNodeStyle>
</LevelStyles>
<RootNodeStyle Font-Bold="True" BackColor="#FFFFFF"></RootNodeStyle>
<ParentNodeStyle ForeColor="#000066" BackColor="#FFFFFF"></ParentNodeStyle>
<HoverNodeStyle Font-Underline="false" BorderColor="#EEEEEE" BackColor="#FFFFFF" ForeColor="#0000FF"></HoverNodeStyle>
<SelectedNodeStyle BorderWidth="1px" ForeColor="#660066" BorderStyle="Solid" BackColor="#FFFFFF"></SelectedNodeStyle>
</asp:TreeView>

<asp:CheckBox runat="server" BackColor="transparent" BorderWidth="0" ForeColor="#000066"></asp:CheckBox>

<asp:RadioButton runat="server" BackColor="transparent" BorderWidth="0" ForeColor="#000066"></asp:RadioButton>

<asp:CheckBoxList runat="server" BackColor="transparent" ForeColor="#000066" BorderColor="#EEEEEE" BorderStyle="Solid" BorderWidth="1pt" CellPadding="5" CellSpacing="1"></asp:CheckBoxList>

<asp:RadioButtonList runat="server" BackColor="#FFFFFF" ForeColor="#000066" BorderColor="#EEEEEE" BorderStyle="Solid" BorderWidth="1px" CellPadding="5" CellSpacing="0"></asp:RadioButtonList>

<asp:DropDownList runat="server" BackColor="#FFFFFF" ForeColor="#000066"></asp:DropDownList>

<asp:ListBox runat="server" BackColor="#FFFFFF" ForeColor="#000066"></asp:ListBox>

<asp:BulletedList BulletImageUrl="images/basicblue_bullet1.gif" runat="server" BackColor="transparent" ForeColor="#000066"></asp:BulletedList>

<asp:Login runat="server" ForeColor="#000000" BorderColor="#CCCCCC" BorderStyle="Solid" BorderWidth="2pt" BackColor="#EEEEEE">
<CheckBoxStyle BorderStyle="None" BorderWidth="1px" BorderColor="Navy" BackColor="#EEEEEE"></CheckBoxStyle>
<FailureTextStyle ForeColor="#000066" BackColor="#EEEEEE"></FailureTextStyle>
<HyperLinkStyle ForeColor="#000066" BackColor="#EEEEEE"></HyperLinkStyle>
<TextBoxStyle Font-Italic="True" BorderColor="#000066" BackColor="#FFFFFF" Forecolor="#000066"></TextBoxStyle>
<InstructionTextStyle Font-Italic="True" BackColor="transparent"></InstructionTextStyle>
<TitleTextStyle Font-Bold="True" ForeColor="#FFFFFF" BackColor="#000066"></TitleTextStyle>
<LabelStyle ForeColor="#000000" BackColor="#EEEEEE"></LabelStyle>
</asp:Login>

<asp:LoginName runat="server" Font-Bold="True" ForeColor="#000066"></asp:LoginName>

<asp:LoginStatus runat="server" ForeColor="#000066" Font-Bold="True" BorderColor="#000066"></asp:LoginStatus>

<asp:SiteMapPath runat="server" ForeColor="#000066" BackColor="#FFFFFF" Bordercolor="#000066">
<CurrentNodeStyle ForeColor="#660066" Font-Bold="true" Font-Underline="false" BorderColor="#FFFFFF" BackColor="#FFFFFF"></CurrentNodeStyle>
<PathSeparatorStyle ForeColor="#000000" Font-Underline="false" BorderColor="#FFFFFF" BackColor="#FFFFFF"></PathSeparatorStyle>
<RootNodeStyle ForeColor="#000066" Font-Underline="true" BorderColor="#FFFFFF" BackColor="#FFFFFF"></RootNodeStyle>
<NodeStyle ForeColor="#000066" Font-Underline="true" BorderColor="#FFFFFF" BackColor="#FFFFFF"></NodeStyle>
</asp:SiteMapPath>

<asp:wordRecovery runat="server" ForeColor="#000000" BorderWidth="2pt" BorderStyle="Solid" BorderColor="#CCCCCC" BackColor="#EEEEEE">
<SubmitButtonStyle BackColor="#EEEEEE" BorderStyle="Solid" BorderColor="#000066" BorderWidth="1pt" ForeColor="#000066"></SubmitButtonStyle>
<HyperLinkStyle ForeColor="#000066" BackColor="#EEEEEE"></HyperLinkStyle>
<FailureTextStyle ForeColor="#000066" BackColor="#EEEEEE"></FailureTextStyle>
<InstructionTextStyle ForeColor="#660066" Font-Italic="true" BackColor="#EEEEEE"></InstructionTextStyle>
<SuccessTextStyle ForeColor="#000066" Font-Bold="true" BackColor="#000000"></SuccessTextStyle>
<TitleTextStyle Font-Bold="True" ForeColor="#FFFFFF" BackColor="#000066"></TitleTextStyle>
<TextBoxStyle ForeColor="#000066" BorderWidth="1pt" borderStyle="Solid" BorderColor="#000066" BackColor="#FFFFFF"></TextBoxStyle>
<LabelStyle ForeColor="#000000" BackColor="#EEEEEE"></LabelStyle>
</asp:wordRecovery>

<asp:Wizard runat="server" ForeColor="#000000" BackColor="#E6E6FA" Bordercolor="#000066" BorderWidth="1pt">
<HeaderStyle ForeColor="#FFFFFF" BackColor="#000066"></headerstyle>
<SidebarStyle ForeColor="#000066"/>
<SideBarButtonStyle BackColor="lavender" ForeColor="#000066" BorderColor="#000066" />
<StepStyle BackColor="#FFFFFF" BorderColor="#000000" ForeColor="#000000" BorderWidth="1pt"/>
<NavigationStyle ForeColor="#000066" BorderColor="#000066"/>
<NavigationButtonStyle ForeColor="#000066" BorderColor="#000066"/>
</asp:Wizard>


Now you have to write code under the Page_PreInit Event:

protected void Page_PreInit(object sender, EventArgs e)
{
string theme = "";
if (Page.Request.Form.Count > 0)
{
theme = Page.Request["Themes"].ToString();
if (theme == "Default2")
{
theme = "";
}
}
this.Theme = theme;
}
}

Now run the application; the Theme will change.