JSFiddle - React, Tailwind, and code Playground

HTML

<style type="text/css">

a.nowandthen{
position:relative;
display: block;
overflow:hidden;
cursor: pointer;
width: 650px; 
height: 434px; 
}

a.nowandthen img{
position:absolute;
left:0;
top:0;
width: 100%;
height: 100%;
-moz-transition: all 0.4s ease; 
-webkit-transition: all 0.4s ease;
-o-transition: all 0.4s ease;
-ms-transition: all 0.4s ease;
transition: all 0.4s ease;
z-index: 2;
clip: rect(0,650px,434px,0);
}


a.nowandthen img:nth-of-type(2){ 
z-index: 1;
}


a.nowandthen:hover img:nth-of-type(1){ 
clip: rect(0,0,434px,0); 
opacity: 0;
}

</style>

<a class="nowandthen" href="http://www.blogger.com/null">
 <img alt="" src="http://2.bp.blogspot.com/-XgMF8m5_I4s/Ua9FXCAkg0I/AAAAAAAAHro/Y5WAydhFEXE/s1600/sunset-sunrise-btrix+(1).jpg" />
 <img alt="" src="http://1.bp.blogspot.com/-VLHb1JqiTWY/Ua9FWGRxVNI/AAAAAAAAHrg/XF1gYctgGSA/s1600/sunset-sunrise-btrix+(2).jpg" />
</a>