I have a Rounded Border containing a ComboBox as follow:

As soon as my mouse hover on the ComboBox, I get this

I want to get rid of the button-like background. I tried setting background to white or null in MouseEnter, MouseLeave, MouseUp… everything with Mouse but still I can’t get rid of the default button background on the ComboBox. Does anyone has a clue?
Code below:
/* XAML */
<Border CornerRadius="11" BorderThickness="1" Height="24" Width="70"
Grid.Column="1" Margin="5,5,5,5" VerticalAlignment="Center"
HorizontalAlignment="Left" Background="White">
<ComboBox x:Name="comboBox1" BorderBrush="{x:Null}"
Background="{x:Null}" Width="70" MouseMove="MouseHover"
MouseEnter="MouseHover"
</ComboBox>
</Border>
/* C# code */
private void MouseHover(object sender, RoutedEventArgs e)
{
comboBox1.Background = null;
}
You have to modify the default controlTemplate of the Combobox for this.Check the link below
http://social.msdn.microsoft.com/Forums/en/wpf/thread/a18891e9-8879-4819-9679-247341782f60