JSFiddle - React, Tailwind, and code Playground

HTML

<div id="button"><div id="plus">+</div></div>

CSS

#button
{
    position : fixed;
    top:0; 
    left:0;
    width : 100px;
    height : 100px;
    background-color : red;
}

    #plus
    {
        position : relative;
        width : 50%;
        height : 50%;
        top:25%;
        margin : 0 auto;
        background:orange;        

    }