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Window style from an external (dll) resource dictionary doesn't apply in design mode

I have create a external control library which hosts some resource dictionaries etc. My problem is when I try to apply a style on a window element. Style's changes become visible only in running mode!!!
An example of the resource dictionary from my control library:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Style x:Key="Window_Style" TargetType="Window">
<Setter Property="Background" Value="#FF272727"/>
</Style>
</ResourceDictionary>
This is how I include my external resource dictionary into my app:
<Application x:Class="SigmaLibMaster.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:SigmaLibMaster"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/SigmaLib;component/Resources/Styles/Window.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
And how I apply it to my window element:
<Window x:Class="SigmaLibMaster.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:SigmaLibMaster"
mc:Ignorable="d"
Title="MainWindow" Height="480" Width="840"
Style="{DynamicResource Window_Style}">
<Grid >
</Grid>
</Window>
Any idea why is this happening?
PS: Please keep in mind that I recently switched from WinForms to WPF!!! :)

You can sometimes find that resources from libraries don't work at design time.
It's a bug IMO.
The work round I use is design time resources.
This is a mechanism which was originally intended for blend. But the wpf designer in visual studio is the same designer as blend now.
I have a library called uilib.
In the properties of that I add a resource dictionary called DesignTimeResources.xaml. It must be that name.
In the csproj I have the following:
<ItemGroup>
<Page Include="Properties\DesignTimeResources.xaml" Condition="'$(DesignTime)'=='true' OR ('$(SolutionPath)'!='' AND Exists('$(SolutionPath)') AND '$(BuildingInsideVisualStudio)'!='true' AND '$(BuildingInsideExpressionBlend)'!='true')">
<Generator>MSBuild:Compile</Generator>
<SubType>Designer</SubType>
<ContainsDesignTimeResources>true</ContainsDesignTimeResources>
</Page>
Note particularly that ContainsDesignTimeResources tag.
That merges a bunch of resource dictionaries I have in uilib:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:UILib">
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/UILib;component/Resources/Geometries.xaml"/>
<ResourceDictionary Source="pack://application:,,,/UILib;component/Resources/ControlTemplates.xaml"/>
<ResourceDictionary Source="pack://application:,,,/UILib;component/Resources/FontResources.xaml"/>
<ResourceDictionary Source="pack://application:,,,/UILib;component/Resources/UILibResources.xaml"/>
<ResourceDictionary Source="pack://application:,,,/UILib;component/Resources/HypsoColoursRD.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
It will not merge these resources in an extra time when you build. The conditions in the tags mean it's design time only.
You can probably find a bunch more on this by searching now you know it exists.
https://dennymichael.net/2016/07/28/wpf-design-time-resources-dictionary/

WPF: Mahapps Metro Watermark is not showing up

I am working on a program, and in the settings I want watermarks to tell the user what he can insert there. I used Mahapps Metro, but the watermarks didn't show up, so I created a blank project with only one textbox, but it still doesn't show up.
My Code:
<Controls:MetroWindow x:Class="TestWPF.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:Controls="http://metro.mahapps.com/winfx/xaml/controls"
xmlns:local="clr-namespace:TestWPF"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid Background="White">
<TextBox Controls:TextBoxHelper.Watermark="TestWater" Height="25" Width="200"/>
</Grid>
</Controls:MetroWindow>
The outcome:
(The background is actually "Wheat" to make the textbox more visible)
Am I missing anything why it doesn't work?

Add this in the App.xaml of the your WPF Project.
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colors.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/Blue.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
I've tried this and this is working fine after this.
Go through the documentation provided here.

WPF Xaml suggesions not working on VS2019 16.4.4

I have a project (WpfControlLibrary1:WPF user control library) which includes MyDictionary.xaml. This dictionary includes resource definitions like :
<SolidColorBrush Color="AliceBlue" x:Key="MY_COLOR"/>"
I have another project(WpfCustomControlLibrary1:WPF custom control library).
WpfCustomControlLibrary1 references WpfControlLibrary1 to use styles. WpfCustomControlLibrary1 has App.xaml file like this.
<Application x:Class="WpfCustomControlLibrary1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/WpfControlLibrary1;component/Dictionary1.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
And I have a UserControl1.xaml in WpfCustomControlLibrary1 like this.
**<UserControl x:Class="WpfCustomControlLibrary1.UserControl1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="450"
d:DesignWidth="800">
<!--Suggestion not working for MY_COLOR-->
<!--Please open the solution in VS 2013 and see the Suggestions working-->
<Button Background="{StaticResource MY_COLOR}" />
</UserControl>**
Every thing is OK. But the problem is Static resource suggestions not working in VS2019.
I'm opening the solution with VS2013. Suggestions working in VS2013

ResourceDictionary in separate library

I have defined my resourceDictionary in a separate library as below
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:cultures="clr-namespace:My_Localization.Cultures"
xmlns:properties="clr-namespace:My_Localization.Properties">
<ObjectDataProvider x:Key="Resources" ObjectType="{x:Type cultures:CultureResources}" MethodName="GetResourceInstance"/>
<ObjectDataProvider x:Key="CultureResourcesDS" ObjectType="{x:Type cultures:CultureResources}"/>
</ResourceDictionary>
I have used this library from another library as below (Header of xaml only)
<msRibbon:RibbonTab x:Class="Ribbon.Planner.PlannerRibbon"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:msRibbon="clr-namespace:Microsoft.Windows.Controls.Ribbon;assembly=RibbonControlsLibrary"
mc:Ignorable="d"
d:DesignHeight="100" d:DesignWidth="500" Header="{Binding Path=Ribbon_About, Source={StaticResource Resources}}"
>
<Grid>
...
...
...
</Grid>
I have added the reference of My_Localization lib and I am only changing the header. All works fine but the only problem is that in design time I have "Header="{Binding Path=Ribbon_About, Source={StaticResource Resources}}" underlined. When I hover my mouse there is hint "The resource "Resources" could not be resolved"
Why is there an error like hint in my xaml? and then why does it all work fine?
My Solution structure
MainExe - Contains app.xaml. I have merged the resource dictionary here. No problems in xaml since the merge dictionary exists in app.xaml
My_Localization - Lib containing the resource dictionary (code above)
Lib1 - References My_Localization and there are problems in xaml as explained
Lib2 - References My_Localization and there are problems in xaml as explained
Lib3 - References My_Localization and there are problems in xaml as explained

You need to provide a reference to the ResourceDictionary either in the app.xaml file or locally. Resources in app.xaml are available globally to all xaml files of the application.
For Xaml files in library projects the designer works a little differently.
At runtime it will be the app.xaml in the startup project that will be used for all assemblies. At designtime it will be the app.xaml of the local assembly.
This means, you can add a app.xaml file to libraies, which will only be used by the Visual Studio Designer when rendering xaml files from that specific library (Set build action of file to Page).
To reference a ResourceDictionary do this:
<Application xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
<Application.Resources>
<ResourceDictionary>
<!-- Other global resources -->
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/ASSEMBLYNAME;component/FOLDERPATH/RDNAME.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
Where ASSEMBLYNAME is the name of the assembly where the ResourceDictionary is (check properties of project).
Example:
Project with assembly name: "MyAssembly" and ResourceDictionary in folder path "Resources/RDs/MyRd.xaml"
Source="pack://application:,,,/MyAssembly;component/Resources/RDs/MyRd.xaml"

In App.xaml, you must add a MergedDictionary to the resources which will reference your other dictionary.
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/RibbonControlsLibrary;component/Your/Dictionary/Path.xaml" />
...
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>

You can include the ResourceDictionary in each xaml
<msRibbon:RibbonTab x:Class="Ribbon.Planner.PlannerRibbon"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:msRibbon="clr-namespace:Microsoft.Windows.Controls.Ribbon;assembly=RibbonControlsLibrary"
mc:Ignorable="d"
d:DesignHeight="100" d:DesignWidth="500" Header="{Binding Path=Ribbon_About, Source={StaticResource Resources}}">
<msRibbon:RibbonTab.Resources>
<ResourceDictionary Source="pack://application:,,,/<ASSEMBLY_NAME>;component/<RESOURCES_FILE>.xaml"/>
</msRibbon:RibbonTab.Resources>
<Grid>
...
...
...
</Grid>

Error visualizing Mahapps metro style

I'm trying to use the Mahapps's Metro Style v1.0 stable in VS2013 with Windows 7. According to the initial modification in the quick start section, the main window should look like this:
but instead look like this:
When I used version 0.7 worked fine.
Has anyone else experienced this?
Interesting fact:
The second image is what I get, it is saved in .jpeg, but when I saved the screenshot in .png format, it looks like this:

You should have always these basic stuff:
App.xaml
<Application x:Class="WpfApplication.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colors.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/Blue.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
Window xaml
<controls:MetroWindow x:Class="WpfApplication.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:controls="http://metro.mahapps.com/winfx/xaml/controls"
Title="MainWindow"
Height="600"
Width="800">
<Grid>
<!-- now your content -->
</Grid>
</controls:MetroWindow>
Window xaml code behind
using System;
using MahApps.Metro.Controls; // MahApps.Metro reference
namespace WpfApplication
{
public partial class MainWindow : MetroWindow
{
public MainWindow()
{
InitializeComponent();
}
}
}
Hope this helps!

You can see how everything is implemented on very simple examples to GitHub MahApps.Metro
Surely you forgot to remove or add what is namespace in xaml page or not remove window parameters.