JSFiddle - React, Tailwind, and code Playground

HTML

<div class="fix">
    <div class="wb">
        <div class="black"></div>
    </div>
</div>
<div class="page"></div>

CSS

html,body{
    margin:0px;
    padding:0px;
    height:100%;
}
.page{
    margin:0px auto;
    width:80%;
    height:200%;
    background:#bbb;
}
.fix{
    position:fixed;
    top:100px;
    left:0px;
    right:0px;
    height:0px;
}
.wb{
    margin:0px auto;
    width:80%;
    height:0px;
}
.black{
    width:50px;
    height:50px;
    background:#000;
}