title: CSS position div exactly over certain image point
body: <p>I have a landscape image of a city sky line which will fill the users viewport at 100% wide, with an automatic height. </p>
  
  <p>I want to position elements on top of that image on exact points of the image (say a particular building roof), but I need those elements to remain over those exact points when the viewport decreases/increases in size.</p>
  
  <p>I've thought of absolutely positioning the elements (with the parent relatively positioned), but they just go "off target" when the viewport changes.</p>
  
  <p>What's the most effective way of doing this?</p>