title: Responsive App: which font-size units em vs. px vs. pt vs. percent
body: <p>I am building a responsive app targeted to desktop, tablet and mobile phone using HTML and CSS but I am not sure what unit font size should I use that the font fits well in any size screen. What's difference between em, px, pt and percent? What's the best choose for me?</p>
  
  <p>I would like to hear real experiences about it in responsive apps for desktop, tablets and mobile phones</p>
  
  <p>I would be thankful for any help!</p>