title: How to add a theme in wpf
body: <p><img src="https://i.stack.imgur.com/LcivY.jpg" alt="error">
  I want to add expressiondark theme on WPF. </p>
  
  <p>in App.xaml:</p>
  
  <pre><code>&lt;Application x:Class="ThemesSample.App" 
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
      StartupUri="MYWINDOW.xaml"&gt; 
      &lt;Application.Resources&gt; 
          &lt;ResourceDictionary Source="ExpressionDark.xaml"/&gt; 
      &lt;/Application.Resources&gt; 
  &lt;/Application&gt; 
  </code></pre>
  
  <p>in MainWindow.cs:</p>
  
  <pre><code>public MainWindow()
  { 
      ResourceDictionary skin = new ResourceDictionary(); 
      skin.Source = new Uri(@"MYPROJECTADDR\ExpressionDark.xaml", UriKind.Absolute); 
      App.Current.Resources.MergedDictionaries.Add(skin); 
  }
  </code></pre>
  
  <p>and added expressiondark.xaml in project. But there are errors all xmlns lines in xpressiondark.xaml. </p>
  
  <p>What is wrong? </p>