Resource dictionary cannot be found? - wpf

Question

At least I think this is the problem...
I have a project structured like so (files omitted for brevity)
Project
Assets
ResourceDictionaries
Styles.xaml
MainWindow.xaml
I am referencing the resource dictionary as follows in MainWindow.xaml
<Window.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Assets/ResourceDictionaries/Styles.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
<Window.Resources/>
But none of the styles are being applied to any elements.
I've checked the Build Action is set to page. I've also tried giving some styles in the dictionary a key, but Blend cannot 'see' these keys.
What am I doing wrong?
Edit: Relevant code. Obviously if I put the properties on the actual elements they work, but in a dictionary they don't:
MainWindowStyles.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Company.Client.Assets.ResourceDictionaries"
xmlns:wpf="http://schemas.syncfusion.com/wpf">
<Style TargetType="{x:Type wpf:RibbonWindow}">
<Setter Property="wpf:SkinStorage.VisualStyle" Value="Office2010Silver"/>
</Style>
<Style TargetType="{x:Type wpf:Ribbon}">
<Setter Property="BackStageColor" Value="#622166"/>
</Style>
</ResourceDictionary>
MainWindow.xaml
<wpf:RibbonWindow x:Class="Company.Client.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:wpf="http://schemas.syncfusion.com/wpf"
xmlns:local="clr-namespace:Company.Client"
mc:Ignorable="d"
Title="MainWindow" Height="600" Width="800">
<wpf:RibbonWindow.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Assets/ResourceDictionaries/MainWindowStyles.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</wpf:RibbonWindow.Resources>
<Grid>
<wpf:Ribbon BackStageHeader="DB">
<wpf:Ribbon.BackStage>
<wpf:Backstage>
<wpf:BackStageCommandButton Header="Save"/>
</wpf:Backstage>
</wpf:Ribbon.BackStage>
</wpf:Ribbon>
</Grid>
</wpf:RibbonWindow>
Edit 2:
This is what has been tried so far:
Tried applying styles to normal controls (Button, Label, etc.). Works
Tried adding the styles under <wpf:MainWindow.Resources>. Doesn't work
Tried a pack URI. Doesn't work
Adding the styles/properties to the actual elements. Works (obviously)

Answer 1

Have you tried these two steps:
Add MainWindowStyles.xaml to Application.Resources section in app.xaml
Use explicit style for RibbonWindow, like this:
<RibbonWindow>
...
<RibbonWindow.Style>
<StaticResource ResourceKey="RadRibbonWindowStyle"/>
<RibbonWindow.Style>

Answer 2

Use the pack URI syntax:
<ResourceDictionary Source="pack://application:,,,/Assets/ResourceDictionaries/Styles.xaml"/>

Answer 3

Adding this to supplement the accepted answer.
My code now looks like this. I didn't manage to get it to work with the VisualStyle property, but this will do. If anyone does know how to get that into a Resource Dictionary though, the help would be much appreciated. :)
Long story short, this is the code that works based on the exchange between me and #AlexSeleznyov
MainWindowStyles.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:wpf="http://schemas.syncfusion.com/wpf">
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Syncfusion.Tools.Wpf;component/framework/ribbon/themes/office2010silverstyle.xaml"/>
</ResourceDictionary.MergedDictionaries>
<Style x:Key="MainRibbon" TargetType="{x:Type wpf:Ribbon}" BasedOn="{StaticResource Office2010SilverRibbonStyle}">
<Setter Property="BackStageColor" Value="#622166"/>
</Style>
</ResourceDictionary>
MainWindow.xaml
<wpf:RibbonWindow x:Class="Company.Client.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:wpf="http://schemas.syncfusion.com/wpf"
xmlns:local="clr-namespace:Company.Client"
mc:Ignorable="d"
wpf:SkinStorage.VisualStyle="Office2010Silver"
Title="MainWindow" Height="600" Width="800"
Icon="Assets/Icons/ApplicationIcon.ico">
<wpf:RibbonWindow.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Assets/ResourceDictionaries/MainWindowStyles.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</wpf:RibbonWindow.Resources>
<Grid>
<wpf:Ribbon BackStageHeader="File" Style="{StaticResource MainRibbon}">
<wpf:Ribbon.BackStage>
<wpf:Backstage>
<wpf:BackStageCommandButton Header="Save"/>
</wpf:Backstage>
</wpf:Ribbon.BackStage>
</wpf:Ribbon>
</Grid>
</wpf:RibbonWindow>