Custom Control Styling/Triggers - wpf

Question

I'm trying to make a custom control that consists of several buttons and a couple labels, but the buttons are supposed to be invisible, showing only the content within them. I can get rid of the border, background, etc by setting them to Transparent. But whenever I MouseOver them the default windows hover effect shows the whole button again. I've tried numerous guides on custom controls, but ultimately cannot figure out how to override this. Basically my questions boil down to, how much of this can be placed in the generic.xaml file, what organization do I have to use within that file, and are there any other places that these styling should go instead? I do realize this is a very basic question, but it's just driving me nuts not being able to figure out the specific answer. Thanks!
Current xaml:
<Style TargetType="{x:Type local:TimePicker}">
<Setter Property="Background" Value="Transparent" />
<Setter Property="BorderBrush" Value="Transparent" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:TimePicker}">
<Border Background="{TemplateBinding Background}"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}"
Height="{TemplateBinding Height}"
Width="{TemplateBinding Width}">
<StackPanel Orientation="Horizontal">
<StackPanel x:Name="PART_Root"
Orientation="Horizontal"
HorizontalAlignment="Center">
<ToggleButton x:Name="PART_HourButton"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Margin="0"
Background="Transparent"
BorderBrush="Transparent"
BorderThickness="0"
Height="{Binding ElementName=PART_IncDecPanel, Path=ActualHeight}"
Width="{Binding ElementName=PART_HourButton, Path=ActualHeight}"
Content="{Binding RelativeSource={RelativeSource TemplatedParent},Path=Hour}">
<ToggleButton.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="Transparent" />
</Trigger>
</ToggleButton.Triggers>
</ToggleButton>
<Label x:Name="PART_HourMinSeparator"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Margin="0"
Content=":" />
<ToggleButton x:Name="PART_MinButton"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Margin="0"
Background="Transparent"
BorderBrush="Transparent"
BorderThickness="0"
Height="{Binding ElementName=PART_HourButton, Path=ActualHeight}"
Width="{Binding ElementName=PART_HourButton, Path=ActualWidth}"
Content="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Minute}" />
<StackPanel x:Name="PART_IncDecPanel" HorizontalAlignment="Center" VerticalAlignment="Center">
<Button x:Name="PART_IncreaseTime"
Background="Transparent"
BorderBrush="Transparent"
BorderThickness="0"
HorizontalAlignment="Center"
HorizontalContentAlignment="Center"
VerticalAlignment="Center"
VerticalContentAlignment="Center"
Margin="0"
Padding="0"
Width="22"
Height="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=IncreaseImage.ActualHeight}">
<Image Source="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=IncreaseImage}" />
</Button>
<Button x:Name="PART_DecreaseTime"
Background="Transparent"
BorderBrush="Transparent"
BorderThickness="0"
HorizontalContentAlignment="Center"
HorizontalAlignment="Center"
VerticalAlignment="Center"
VerticalContentAlignment="Center"
Margin="0"
Padding="0"
Height="{Binding ElementName=PART_IncreaseTime, Path=ActualHeight}"
Width="{Binding ElementName=PART_IncreaseTime, Path=ActualWidth}">
<Image Source="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=DecreaseImage}" />
</Button>
</StackPanel>
</StackPanel>
</StackPanel>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 1

WPF uses "lookless controls," which basically means that you can change the entire visual part (at design- or run-time) of a control without changing its code or the behavior of that code. You're already making use of this concept to create a default Style for your TimePicker control. If you were to remove the ControlTemplate from that Style, you would see nothing at runtime because the control itself is just the behavior defined in the C# or VB code.
Since it sounds like you want to keep the behavior of your buttons, but completely change the look, this is an ideal scenario for re-templating. Here's a very simple example that will show only the Content (in the ContentPresenter):
<Button Content="Hello Template">
<Button.Template>
<ControlTemplate TargetType="{x:Type Button}">
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</ControlTemplate>
</Button.Template>
</Button>
You will probably want to add some more to the template, like a Transparent Border to catch mouse input and maybe some Triggers. The way you're attempting to use a Trigger on the ToggleButton in your example is incorrect (FrameworkElement Triggers collection only works with EventTriggers), but inside a ControlTemplate or Style, that pattern will work.
If you want to apply the same Style to every Button inside your TimePicker ControlTemplate you can add a default Button Style to the Resources collection of your ControlTemplate:
<ControlTemplate TargetType="{x:Type MyControl}">
<ControlTemplate.Resources>
<Style TargetType="{x:Type Button}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ControlTemplate.Resources>
...
</ControlTemplate>