Personally, I throw all my resource dictionaries in one place. Then map them via an app.xaml in each project using
ResourceDictionary.MergedDictionaries which will often require a source string like / similar to.
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Your.Project.Name;component/Resources/Styles/YourStyles.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
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