title: what is different between devicePixelRatio and dppx?
body: <p>I have do some research about <code>devicePixelRatio</code> and <code>dppx</code>:</p>
  
  <p><code>deicePixelRatio</code>: returns the ratio of the (vertical) size of one physical pixel on the current display device to the size of one CSS pixel.</p>
  
  <p><code>dppx</code>: dots per ‘px’ unit.</p>
  
  <p>I think they are just the same thing, but I am not sure, am I right?</p>