WPF: Use multiple resources to target the same element or control - wpf

Question

I would like to know if it is possible to use multiple resources to target the same element or control in WPF? I noticed that the XAML file cascade and the next XAML file in the resources list will overtake the next one if the same elements are targeted.
is it possible to get around this?
What I am trying to do is have one XAML file be my layout and positioning and one be strictly used for colors.
In my App.xaml My resources area as follows:
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Views/LayoutAndPositioning/LayoutAndPositioning.xaml"/>
<ResourceDictionary Source="/Views/Theme/DefaultColors.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
LayoutAndPositioning.xaml for element
<Style x:Key="MyElement" TargetType="{Rectangle}">
<Setter Property="Margin" Value="200,200,200,200" />
</Style>
DefaultColors.xaml for element
<Style x:Key="MyElement" TargetType="{Rectangle}">
<Setter Property="Fill" Value="Green" />
<Setter Property="Width" Value="400" />
<Setter Property="Height" Value="200" />
</Style>
But when I try to target the same element in the 2 different files. The LayoutAndPositioning.xaml, which is first in the list, does not apply to the element since the DefaultColors.xaml does not have position styles in it. The DefaultColors.xaml does not have margin so my element just ends up having no margin property.
I have tested taking out the DefaultColors.xaml from the App.xaml resource list and the positioning returns. So it seems to be a cascading thing.
Does anyone have any ideas if it is possible to target the same element in 2 different Xaml files.

Answer 1

Try doing the following:
Merge LayoutAndPositioning.xaml into DefaultColors.xaml by doing the following at the to op DefaultColors.xaml
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Views/LayoutAndPositioning/LayoutAndPositioning.xaml"/>
</ResourceDictionary.MergedDictionaries>
Remove LayoutAndPositioning.xaml from your Application.Resources
Then change:
<Style x:Key="MyElement" TargetType="{Rectangle}">
<Setter Property="Fill" Value="Green" />
<Setter Property="Width" Value="400" />
<Setter Property="Height" Value="200" />
</Style>
To
<Style x:Key="RectStyle" TargetType="{Rectangle}" basedOn="{StaticResource MyElement}">
<Setter Property="Fill" Value="Green" />
<Setter Property="Width" Value="400" />
<Setter Property="Height" Value="200" />
</Style>