Javascript add scripts to center the <div> element

Source Code: (back to article)

<!DOCTYPE html>
<html>
  <head>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.0/jquery.min.js"></script>
    <style>
      div.box {
        width: 400px;
        height: 300px;
        border: 2px solid green;
        position: relative;
        top: 10px;
        left: 10px;
      }
      div.myclass {
        width: 50px;
        height: 50px;
        color: white;
        background: green;
        border-radius: 4px;
        text-align: center;
        display: flex;
        align-items: center;
        justify-content: center;
      }
    </style>
  </head>
  <body>
    <div class="box">
      <div class="myclass">Box</div>
    </div>
    <script>
      $(document).ready(function() {
          jQuery.fn.center = function(parent) {
            if(parent) {
              parent = this.parent();
            } else {
              parent = window;
            }
            this.css({
              "position": "absolute",
              "top": ((($(parent).height() - this.outerHeight()) / 2) + $(parent).scrollTop() + "px"),
              "left": ((($(parent).width() - this.outerWidth()) / 2) + $(parent).scrollLeft() + "px")
            });
            return this;
          }
          $("div.myclass:nth-child(1)").center(true);
        });
    </script>
  </body>
</html>