JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div class="must-center"></div>
</body>

CSS

body{
        position: absolute;
        margin: 0;
        box-sizing: border-box;
        width: 100%;
        height: 100%;
    }
    .must-center{
        position:absolute;
        left:0;
        right: 0;
        margin-left: auto;
        margin-right: auto;
        top: 50%;
        transform: translateY(-50%);
        background-color: #f90;
        width: 100px;
        height: 100px;
    }