title: CSS - website overlay when page is loaded
body: <p>Im setting up a website with a different navigation structure compared to whats traditional, and i want to add a overlay on top of the site which is loaded when the user enters the site the first time. </p>
  
  <p>The overlay should be fullscreen, black "opacity=50", and im going to add simple text about how to use the website. It should also go away when klicking</p>
  
  <p>Im a web designer, and i have limited knowledge in coding. (some css/html/php)</p>
  
  <p>Is there a simple way to add a class for this?</p>
  
  <p>Thanks for feedback</p>