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HTML

            
              <div class="box"></div>
            
          
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CSS

            
              .box {
  width: 150px;
  height: 150px;
  background: red;
  margin-top: 20px;
  margin-left: auto;
  margin-right: auto;
  -webkit-transition: background-color 2s ease-out;
  -moz-transition: background-color 2s ease-out;
  -o-transition: background-color 2s ease-out;
  transition: background-color 2s ease-out;
}

.box:hover {
  background-color: green;
  cursor: pointer;
}
            
          
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JS

            
              
            
          
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