title: Menu div filtering
body: <p>First of all, I am beginner with JS. I need somebody to give me info how understand one thing.</p>
  
  <p>I have menu which has got 3 categories and divs. Every div has got one or two categories. What I need is make something like filter - if you select RED on menu, show all divs with class .RED; if you select RED and BLUE, show all divs with both classes .RED and .BLUE.</p>
  
  <p>I know that this is connected with JSON, but how to start and understand it? Please show me some examples on Codepen to better understand this topic.</p>
  
  <p>Thanks!</p>