title: Page looks differently between html file and html inside php file
body: <p>I've created a simple html and it looks perfectly
  But when I use it as maintenance for my wordpress site it has lesser height that expected. CSS and inner HTML are completely the same, I've just inserted html inside maintenance.php
  There are some screens to show what I mean:</p>
  
  <p><img src="https://i.stack.imgur.com/pd5gm.png" alt="Just HTML">
  <img src="https://i.stack.imgur.com/uftA0.png" alt="HTML inside php"></p>
  
  <p>The problems seems to be that  height is not full screen, but I can't tell the difference</p>