JSFiddle - React, Tailwind, and code Playground

HTML

<div class="bg">Наведи на меня
     <div class="test"></div>
</div>

CSS

.test{
    float:left;
    background:green;
    width:100px;
    height:100px;
    margin:auto;
    
}

.bg {
    background: #ccc;
    width:500px;
    height:500px;

}

.bg:hover .test {
     background: #000;

}