JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE>
<html>
<head>
    <title>position center</title>
</head>
<body>
<div id="demo_1"></div>
</body>
</html>

CSS

body{
    height: 100%;
    position: relative;
}
#demo_1{
    position: fixed;
    top: 50%;
    left: 50%;
    margin-left: -100px;
    margin-top: -100px;
    height: 500px;
    width: 400px;
    background-color: red;
}