在VB.NET中自定义SliderExtender不起作用

Question

在我的.aspx页中，我正在使用AJAX SliderExtender控件。它很好用，但看起来很基本，所以我想尝试自定义样式，但无法使其正常工作。这是我尝试的代码：

Dim slidext_sliderBox_SliderExtender As New SliderExtender
With slidext_sliderBox_SliderExtender
    .ID = "slidext_sliderBox_SliderExtender_" & idx.ToString
    .Maximum = 10
    .Minimum = 0
    .TargetControlID = "txtboxSliderBox_" & idx.ToString
    .RaiseChangeOnlyOnMouseUp = False
    .Length = 310
    Dim NewStyle As New HtmlGenericControl
    With NewStyle
        .TagName = "style"
        .Attributes.Add("type", "text/css")
        .Attributes.Add("id", "ajax__slider_h_railNEW")
        .Attributes.Add("runat", "server")
        .InnerText = "ajax__slider_h_railNEW {position: absolute; background: url('Images/dot.gif') repeat; height: 18px; width: 50px;}"
        .InnerHtml = "ajax__slider_h_railNEW {position: absolute; background: url('Images/dot.gif') repeat; height: 18px; width: 50px;}"
    End With
    Page.Header.Controls.Add(NewStyle)
    .RailCssClass = "ajax__slider_h_railNEW"

结果是导轨消失了，只有手柄出现在控件所在的左下角。