<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="" Height="120" Width="240">
<Window.Resources>
<Style TargetType="{x:Type Button}">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="FontWeight" Value="Bold" />
</Trigger>
</Style.Triggers>
</Style>
</Window.Resources>
<StackPanel Margin="8">
<Button Height="25" Width="100" Margin="4">
Mouse Over Me!
</Button>
</StackPanel>
</Window>
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