<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>

    <div class="box"></div>
    <div class="box2"></div>
  .box {
       width: 75px;
    height: 75px;
    margin: auto;
    background-color: #ffff6b;
  }

  .box2 {
    display: none;
      width: 75px;
    height: 75px;
    margin: auto;
    background-color: red;
  }
$(function() {
  $('.box').mouseover(function () {
    $('.box2').fadeIn(2000);
  });
});

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.