'Font Awesome' в медиа запросах

footer { 
  text-align: center; 
} 
 
footer .fa { 
  font-size: 1rem; 
  margin: 0 1rem; 
} 
 
@media screen and (min-width: 420px){ 
  footer .fa { 
    font-size: 2rem; 
  } 
}

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css" /> 
 <footer> 
   <i class="fa fa-facebook" aria-hidden="true"></i> 
   <i class="fa fa-git" aria-hidden="true"></i> 
   <i class="fa fa-stack-overflow" aria-hidden="true"></i> 
   <i class="fa fa-vk" aria-hidden="true"></i> 
 </footer>