JSFiddle - React, Tailwind, and code Playground

CSS

.-black {
  background: #000;
}

JavaScript

var mq = matchMedia('(max-width: 768px)');

var handler = function(e) {
	
  if (e.matches) {
  	
    document.body.classList.add('-black');
  
  }
  else {
  
  	document.body.classList.remove('-black');
  
  }
  
};

mq.addListener(handler);

handler(mq);