title: Apply Theme/Dynamic CSS to a Page/any HTML Element
body: <p>At some point, Users might get bored of the <code>Style/Theme</code> of the <code>WEB applications</code>.<br>
  They might think, "<strong>Only If I could make it look the way I like it</strong>"<br></p>
  
  <p><strong>example</strong>:</p>
  
  <ul>
  <li>I myself is a user of Stack Overflow. What if I Like the Page-headerBar to look Blue/Purple</li>
  <li>Page itself to have a Black background and white text color</li>
  <li>...</li>
  </ul>
  
  <p><strong>My need</strong>:<br>
  Not just change the class attribute but the complete CSS definition itself.<br>
  If we force the users to select from a set of Stylesheets, that would be constricting them to a small space, So I like to avoid that.</p>
  
  <p><strong>* Note *</strong> I need it in pure javascript not using any jquery plugin or any jquery script</p>