JSFiddle - React, Tailwind, and code Playground

HTML

<div class="menu">
    <div class="base">1</div>
    <div class="active">2</div>
</div>

CSS

/* base styles */
.menu .active {
    display: none;
}

.menu:hover .active {
    display: block;
}

.menu:hover .base {
     display: none;
}

/* additional styles */
.menu {
    background: red;
    width: 50px;
    height: 50px;
    line-height: 50px;    
    text-align: center;
}