SOURCE

<div class="gallery-item">
  <div class="gallery-icon">
     <a href="http://cyanflower.com/wp-content/uploads/2019/04/b97303b51a4812d.jpg"><img width="300" height="300" src="http://cyanflower.com/wp-content/uploads/2019/04/b97303b51a4812d-300x300.jpg" class="attachment-medium size-medium gallery-image" alt="" srcset="http://cyanflower.com/wp-content/uploads/2019/04/b97303b51a4812d-300x300.jpg 300w, http://cyanflower.com/wp-content/uploads/2019/04/b97303b51a4812d.jpg 600w" sizes="(max-width: 300px) 100vw, 300px"></a>
  </div>  
</div>

.gallery-item {
  overflow: hidden;
}

.gallery-icon img 
{
transition:all .2s ease-in-out;
-webkit-transition:all .2s ease-in-out;
-moz-transition:all .2s ease-in-out;
-ms-transition:all .2s ease-in-out;
-o-transition:all .2s ease-in-out;
}

.gallery-icon:hover img 
{
transform:scale(1.1);
-webkit-transform:scale(1.1);
-moz-transform:scale(1.1);
-ms-transform:scale(1.1);
-o-transform:scale(1.1)
}