JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <button class="subm" type="button">hello</button>
</div>

CSS

.subm {
    position:absolute;
    width:130px;
    top: calc(50% - 13px);
    left: calc(50% - 65px);
    height:25px;
}
#wrapper {
    width: 200px;
    height: 200px;
    border: 1px solid black;
    position: relative;
}