JSFiddle - React, Tailwind, and code Playground

HTML

<div class='box_01' onmouseover="this.style.backgroundColor='blue'"
onmouseout="this.style.backgroundColor='#CCCCCC'"></div>

CSS

.box_01 {
width:255px; background-color:#CCCCCC; height:100px; border:2px solid #FF0000    
}