title: Opacity affecting the whole content
body: <p>How does twitter implement this kind of transparency ? </p>
  
  <p><img src="https://i.stack.imgur.com/cla62.png" alt="enter image description here"></p>
  
  <p>I tried adding opacity to my code but every children element is being affected. what I aim   is somewhat like in the image above. how would I do that? is opacity the right css rule for that?</p>