title: Change style of selected Text in RichTextBox
body: <p>How can I change styles (such as Font, FontSize, Brush) of selected Text in <code>RichTextBox</code> ?</p>
  
  <p><strong>Update :</strong> Let's say I've a <code>RichTextBox</code> and a Toolbar. User comes and select text inside the RichTextBox box and change the font size from toolbar. I want to change style of selected text.</p>