JSFiddle - React, Tailwind, and code Playground

HTML

<div class="mainDiv">
        <div class="player"></div>
        <div class="bar"></div>
        <div class="ai"></div>
        <div class="ball"></div>
    </div>

CSS

.mainDiv {
        display: block;
        position: absolute;
        margin: auto;
        top: 0;
        bottom: 0;
        left: 0;
        right: 0;
        background-color: black;
        width: 600px;
        height: 400px;
    }
    .player {
        position: absolute;
        background-color: #FFF;
        width: 5px;
        height: 70px;
        margin: 20px 0 0 10px;
        padding: 0 0 0 0;
    }
    .bar {
        top: 30px;
        height: 100%;
        width: 5px;
        border-style: dashed;
        border-left: 5px;
        border-color: #FFF;
        position: fixed;
        left: 50%;
    }
    .ai {
        position: absolute;
        right: 10px;
        background-color: #FFF;
        width: 5px;
        height: 70px;
        margin: 164px 0 0 10px;
        padding: 0 0 0 0;
    }

    .ball {
        position: absolute;
        left: 50px;
        bottom: 69px;
        width: 20px;
        height: 20px;
        border-radius: 50%;
        background-color: #FFF;
    }

JavaScript

var playerPosition = 0;

window.onkeyup = function(e) {
    var key = e.keyCode ? e.keyCode : e.which;

    if(key == 38) {
        playerPosition -= 30;

    } else if(key == 40) {
        playerPosition += 30;
    }

    document.getElementsByClassName('player')[0].style.marginTop = playerPosition+"px";

 }