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HTML

            
              <div class="img-wrapper">
  <img class="thumbnail" src="http://placekitten.com/400/200" alt="thumbnail">
</div>
            
          
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CSS

            
              .img-wrapper {
  width: 400px;
  height:200px;
}
.thumbnail {
  width: 400px;
}

.thumbnail {
  -webkit-transition: all 0.2s ease-out;
  -moz-transition: all 0.2s ease-out;
  transition: all 0.2s ease-out;
}

.thumbnail:hover {
  width: 500px;
  
  -webkit-transition: all 0.2s ease-out;
  -moz-transition: all 0.2s ease-out;
  transition: all 0.2s ease-out;
}
            
          
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JS

            
              
            
          
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