Design-time-only background color in WPF?

Question

In WPF XAML there is the convenient DesignHeight and DesignWidth, for instance in code as

Answer 1

The d:DesignerProperties.DesignStyle technique shown on this page works great for applying a WPF design-time-only style to a single control, but it doesn't appear to work for a Style in a ResourceDictionary that would apply to all of the appropriately-typed controls or elements under the scope of the dictionary. Below is simple solution I found for deploying a designer-only style into a ResourceDictionary.

Consider for example a Window containing a TreeView, where we want the TreeViewItem nodes to show as fully expanded—but only at design time. First, put the desired style in the XAML dictionary in the normal way.

Here, the Style is put in the ResourceDictionary of the Window but of course you could use any other subsuming dictionary instead. Next, in the C# code, remove the style from the Resource­Dict­ionary when design mode is not detected. Do this is in the OnInitialized override:

protected override void OnInitialized(EventArgs e)
{
    if (DesignerProperties.GetIsInDesignMode(this) == false)
        Resources.Remove(typeof(TreeViewItem));

    base.OnInitialized(e);
}

Design Mode:                                                        Runtime Mode: