title: WPFToolkit CheckComboBox width issue
body: <p>I'm using the CheckComboBox (from <a href="http://wpftoolkit.codeplex.com/" rel="nofollow noreferrer">Extended WPF Toolkit</a>) in an app, and I'd like to make the "textBox" where it shows the selected items a bit wider, (in fact, I want it to fill all the CheckComboBox) but I'm don't have any idea about how to apply the styles.</p>
  
  <p><img src="https://i.stack.imgur.com/YfZ7h.jpg" alt="CheckComboBox with the problem"></p>
  
  <p>Any help?</p>
  
  <p>Thanks!</p>
  
  <hr>
  
  <p>Current code</p>
  
  <pre><code> &lt;UserControl
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"&gt;
   &lt;!-- ... --&gt;
   &lt;Label Content="Locale: "/&gt;
   &lt;xctk:CheckComboBox Name="LocaleSelector" ItemsSource="{Binding Locales}" ValueMemberPath="Id" SelectedValue="{Binding SelectedLocales}" Margin="5 2 0 2" /&gt;
  </code></pre>