JSFiddle - React, Tailwind, and code Playground

HTML

<img src="http://freshysites1.wpengine.com/wp-content/uploads/2013/10/logo.png">

CSS

img {
    opacity: 1.0; /* Change this to .5 for 50% opacity */
    -webkit-transition: .5s;
       -moz-transition: .5s;
        -ms-transition: .5s;
         -o-transition: .5s;
            transition: .5s;
}
img:hover {
    opacity: .5;
}