title: Cannot remove the margin between the panel and the top of the page with scss in Vaadin
body: <p>I would like to use a Panel as the content for my UI and not a Window, but I still would like to have the header part that exists in the Window class. So I tried this but it does not work perfectly:</p>
  
  <pre><code>@Theme("mytheme")
  @CDIUI("")
  public class MyUI extends UI {
  
      @Inject
      private CDIViewProvider provider;
  
      @Override
      protected void init(VaadinRequest request) {
          Navigator navigator = new Navigator();
          navigator.addProvider(provider);
          navigator.navigateTo("mypanel");  
      }   
  }
  </code></pre>
  
  <p>Then, in my MyPanel class I set the header as a panel like this;</p>
  
  <pre><code>@CDIView("mypanel")
  public class MyPanel extends com.vaadin.ui.Panel implements View {
      @Inject
      private MySubPanel mySubPanel;    
  
      @Override
      public void enter(ViewChangeListener.ViewChangeEvent event) {
          FormLayout layout = new FormLayout();
          Panel headerPanel = new Panel();
          headerPanel.addStyleName("header-panel");
          layout.addComponent(headerPanel);
          layout.addComponent(mySubPanel);
          this.setContent(layout);
      }
  }
  </code></pre>
  
  <p>And finally, in <code>mytheme.css</code> I have the following:</p>
  
  <pre><code>@import "../valo/valo.scss";
  @mixin mytheme {
     // some scss code
  }
  
  .header-panel {
     height: 50px;
     width: 100%;
     background: red repeat-x;
     margin: 0px;
     padding-top: 0px;
  }
  </code></pre>
  
  <p>The <code>headerPanel</code> appears with the correct measures and background color but it is still a small empty, white space above the panel and to the left of it. How can I remove that margin? </p>