title: Flat button in WPF - trigger not firing
body: <p>I wanted to restyle my buttons to be more flat so I have created two styles; first for <code>ToggleButton</code> that derives from <code>ToolBar.ToggleButtonStyleKey</code> and second for <code>Button</code>that derives from <code>ToolBar.ButtonStyleKey</code>.</p>
  
  <p>It worked great - the buttons are now toolbar-like and flat. Second thing I wanted is to have <code>Background</code> property to be transparent when user hovers the cursor over the control. So to achieve that I defined a simple trigger that sets the <code>Background</code> to <code>Transparent</code> on <code>IsMouseOver</code> event. It worked for <code>ToggleButton</code>, however, the same trigger didn't work for <code>Button</code>(the background was not affected at all).</p>
  
  <p>Does anyone know why this trigger works great for <code>ToggleButton</code> and does not work for <code>Button</code>? I did expect the same behavior since both styles are from the same family.</p>
  
  <p>Below is the full code.</p>
  
  <pre><code>&lt;Window x:Class="WpfButtonsTest.MainWindow"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      Title="MainWindow" Height="350" Width="525"&gt;
    &lt;Window.Resources&gt;
  &lt;Style x:Key="FlatToggleButton"  TargetType="ToggleButton" 
  BasedOn="{StaticResource {x:Static ToolBar.ToggleButtonStyleKey}}"&gt;
    &lt;Setter Property="BorderThickness" Value="0"/&gt;
    &lt;Setter Property="Focusable" Value="False"/&gt;
    &lt;Setter Property="Background" Value="Transparent"/&gt;
    &lt;Style.Triggers&gt;
      &lt;Trigger Property="IsMouseOver" Value="True"&gt;
        &lt;Setter Property="Background" Value="Transparent"/&gt;
      &lt;/Trigger&gt;
    &lt;/Style.Triggers&gt;
  &lt;/Style&gt;
  
  &lt;Style x:Key="FlatButton"  TargetType="Button" 
  BasedOn="{StaticResource {x:Static ToolBar.ButtonStyleKey}}"&gt;
    &lt;Setter Property="BorderThickness" Value="0"/&gt;
    &lt;Setter Property="Focusable" Value="False"/&gt;
    &lt;Setter Property="Background" Value="Transparent"/&gt;
    &lt;Style.Triggers&gt;
      &lt;Trigger Property="IsMouseOver" Value="True"&gt;
        &lt;Setter Property="Background" Value="Transparent"/&gt;
      &lt;/Trigger&gt;
    &lt;/Style.Triggers&gt;
  &lt;/Style&gt;
   &lt;/Window.Resources&gt;
   &lt;Grid&gt;
  &lt;StackPanel&gt;
    &lt;ToggleButton Style="{StaticResource FlatToggleButton}"&gt;
      I am Toggle Button
    &lt;/ToggleButton&gt;
  
    &lt;Button Style="{StaticResource FlatButton}"&gt;
      I am Button
    &lt;/Button&gt;
  &lt;/StackPanel&gt;
    &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>