title: how to change color of a page in rails
body: <p>I have a simple rails app with users and post modal, what i want to do is to add a simple button on the show page of each post, which when a user click will change the color of the whole page to a dull greyish color from the usual white one. It will be much like a reading mode for the user.
  Each user can go to reading mode only for themselves not for other users who visits the same post.</p>
  
  <p>I tried searching the internet but found nothing more the <em>how to change button colors.</em></p>