JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent">
    <div class="under">aaa</div> 
    <div class="over">aaa</div>
</div>

CSS

#parent {
    width: 300px;
    height: 300px;
    position relative;
}
.under {
    position: absolute;
    width: 300px;
    height: 300px;
    background: red;
    color: white;    
}
.over {
    position: absolute;
    width: 300px;
    height: 300px;
    bottom:270px;
    background: black;
    color: white;
    transition: 0.3s;
}
#parent:hover .over {
    height: 0px;
    transition: 0.3s;
}