<script>
  function show(viewProductBtn){
document.getElementByClassName(viewProductBtn).style.visibility = "visible";
}

function hide(viewProductBtn) {
document.getElementByClassName(viewProductBtn).style.visibility = "hidden";
}
</script>

<!--HTML-->
<div class="product-shot-bg" onMouseOver="show('viewProductBtn')"      onMouseOut="hide('viewProductBtn')">
        <a href="#" class="viewProductBtn"></a>