JSFiddle - React, Tailwind, and code Playground

HTML

<a >
      <img id="passo1" class="passo" src="http://img2.wikia.nocookie.net/__cb20140902050035/pokemon/images/b/b1/025Pikachu_XY_anime_3.png" style="float:left"/>
  </a>

CSS

.passo {
    filter: gray; /* IE6-9 */
    filter: grayscale(1); /* Firefox 35+ */
    -webkit-filter: grayscale(1); /* Google Chrome, Safari 6+ & Opera 15+ */
    position:absolute;   
    transition:0s 180s;
}

.passo:hover {
   filter: none;
   -webkit-filter: grayscale(0);
   transition:0s;
}