Edit in JSFiddle

// find elements
var banner = $("#banner-message")
var button = $("button")

// handle click and add class
button.on("click", function(){
  banner.addClass("loading");
  setTimeout(function(){
  	banner.removeClass('loading')
  }, ((Math.random() * 5000) + 2000)
  )
});

<div id="banner-message">
  <p>Hello World</p>
  <button>Show Loading</button>
</div>

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#banner-message {
  position: relative;
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  font-size: 25px;
  text-align: center;
  transition: all 0.2s;
  margin: 0 auto;
  width: 300px;
}

button {
  background: #0084ff;
  border: none;
  border-radius: 5px;
  padding: 8px 14px;
  font-size: 15px;
  color: #fff;
}

@keyframes spin {
  0% {
    transform: translate(-50%, -50%) rotate(0deg);
  }
  100% {
    transform: translate(-50%, -50%) rotate(360deg);
  }
}

#banner-message.loading::after {
   position: absolute;
   width: 48px;
   height: 48px;
   content: '';
   left: 50%;
   top: 50%;
   transform: translate(-50%, -50%);
   border-left: solid 3px #fff;
   border-radius: 50%;
   animation: spin .5s linear infinite;
}

#banner-message.loading::before {
    position: absolute;
    width: 100%;
    height: 100%;
    background: rgba(10,10,10,.5);
    content: '';
    left: 0;
    top: 0;
}