JSFiddle - React, Tailwind, and code Playground

HTML

<h1>
  Search and Mark
</h1>

<input type="text" id="search"/>
<button onClick="search(id)" id="button">
Highlight
</button>

<p id="text">
Alongside HTML and CSS, JavaScript is one of the core technologies of the World Wide Web. JavaScript enables interactive web pages and is an essential part of web applications. The vast majority of websites use it for client-side page behavior, and all major web browsers have a dedicated JavaScript engine to execute it.(This excerpt was taken from Wikipedia)
</p>

CSS

*{
  font-family: sans-serif;
}
.{
  background-color: #efefef;
}

JavaScript

function search(e) {
	let searched = document.getElementById("search").value.trim();
  if (searched !== "") {
  	let text = document.getElementById("text").innerHTML;
  	let re = new RegExp(searched,"g"); // search for all instances
		let newText = text.replace(re, `<mark>${searched}</mark>`);
		document.getElementById("text").innerHTML = newText;
  }
}