I believe you have to name the style and apply it to each window like the following..
In app.xaml/resources..
<Style x:Key="MyWindowStyle" TargetType="Window">
<Setter Property="WindowStyle" Value="None"></Setter>
</Style>
Then in the window.xaml..
<Window x:Class="MusicRepo_Importer.MyWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
Title="MyStyledWindow" Style="{StaticResource MyWindowStyle}">
This should work, but simply applying the style with TargetType for Window in the resource won't force the Window to use that style although it seems to work for other elements.
Edit:
Found some info in relation to applying default styles to a window element..
If you supply a TargetType, all
instances of that type will have the
style applied. However derived types
will not... it seems. <Style
TargetType="{x:Type Window}"> will not
work for all your custom
derivations/windows. <Style
TargetType="{x:Type local:MyWindow}">
will apply to only MyWindow. So the
options are
Use a Keyed Style that you specify as
the Style property of every window you
want to apply the style. The designer
will show the styled window.
From the Question: How to set default WPF Window Style in app.xaml?
The person who answered the question had a interesting idea about inheriting from a base window that has the style applied.