JSFiddle - React, Tailwind, and code Playground

HTML

<div class="conjunto">
    <div class="box">Título</div>
    <div class="conteudo">Lorem ipsum set dolor sit amet</div>
</div>

CSS

/* 'Função' */
.conteudo{
    display: none;
}
.conjunto:hover > .conteudo{
    display: block;
    -webkit-transition: all 0.2s ease-in-out;
    -moz-transition: all 0.2s ease-in-out;
    -ms-transition: all 0.2s ease-in-out;
    transition: all 0.2s ease-in-out;
}

/* Estilo */
.conjunto{
    background: #2196F3;
    width: 200px;
    padding: 10px;
    color: #FFF;
}
.box{
    cursor: pointer;
}