JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <div class="arrow">
    </div>
    <div class="arrow right">
    </div>
</div>

CSS

#wrapper {
    background: #000;
    overflow: hidden;
    width: 600px;
    height: 400px;
    position: relative;
}
.arrow {
    overflow: hidden;
    height: 100%;
    position: absolute;
    top: 0;
    width: 50px;
    background: #F00;
    display: block;
    opacity: 0;
}
.right {
    right: 0;
}

JavaScript

$('#wrapper').hover(function() {
    $('.arrow').stop().animate({opacity:1},'slow');
}, function() {
    $('.arrow').stop().animate({opacity:0},'slow');
});