Как работает кнопка

$(document).ready(

  function () {

    $(".button").click(
    function() {
      var display_v = $(".popup").css("display");
      var popup = $(".popup");

      if (display_v == "none"){
        popup.css({"display":"block"});
      } else if (display_v == "block"){
        popup.css({"display":"none"});
      }
    });
  }
);

.button {
  display: inline-block;
  border-radius: 4px;
  background-color: #f4511e;
  border: none;
  color: #FFFFFF;
  text-align: center;
  font-size: 28px;
  padding: 20px;
  width: 200px;
  transition: all 0.5s;
  cursor: pointer;
  margin: 5px;
}

.button span {
  cursor: pointer;
  display: inline-block;
  position: relative;
  transition: 0.5s;
}

.button span:after {
  content: '\00bb';
  position: absolute;
  opacity: 0;
  top: 0;
  right: -20px;
  transition: 0.5s;
}

.button:hover span {
  padding-right: 25px;
}

.button:hover span:after {
  opacity: 1;
  right: 0;
}

/* The message 'box' */
.popup {
  width: 200px;
  text-align: center;
  background-color: #ffffff;
  display: none;
}

<script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<button class = "button" style = "vertical-align:middle"><span>Hover </span></button>

<div class = "popup">
  <p>The messages go here</p>
</div>