JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container"><div id="header" class="header">Hello World</div></div>

CSS

.container{
    height:2000px;
    width:100%;
    background-color:yellow;
    
}

.header{
    text-align:center;
    background-color:red;
    height:100px;
    min-height:50px;
    width:100%;
}

JavaScript

window.onscroll=function () {
    var top = window.pageXOffset ? window.pageXOffset : document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop;
    if(top > 50){document.getElementById("header").style.position = "fixed";
    document.getElementById("header").style.height="50px"
        }
        else {
        document.getElementById("header").style.position = "relative";
    document.getElementById("header").style.height="100px"
        }
}