JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">	
	<link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-gH2yIJqKdNHPEq0n4Mqa/HGKIhSkIHeL5AyhkYV8i59U5AR6csBvApHHNl/vI1Bx" crossorigin="anonymous">
	<link rel="stylesheet" href="js_style.css" />
	<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js" integrity="sha384-A3rJD856KowSb7dwlZdYEkO39Gagi7vIsF0jrRAoQmDKKtQBHUuLZ9AsSv4jD4Xa" crossorigin="anonymous"></script>
	<script src="lesson25.js"></script>
</head>
<body>
	<div id="fragment_25" style="margin-top:50px;">
		<div class="container">
			<div class="row">
				<div class="col-lg-12">
					<form>
						<textarea id="textarea_25" cols="35" rows="5">Привет олень</textarea><br><br>
						<input type="text" placeholder="Введите слово" id="slovo_25">
						<input type="button" value="Найти" onclick="myFrag()" style="margin-bottom:20px;">
					</form>
					<div class="text_25">
						<h3 class="vivod_25"></h3>
					</div>
				</div>
			</div>
		</div>
	</div>
</body>
</html>

JavaScript

function myFrag() {
	// body...
	var vivod = document.querySelector('.vivod_25');
	var text = document.getElementById('textarea_25').value;
	var slovo = document.getElementById('slovo_25').value;
	var text_len = text.length;
	
	if(slovo == ''){
		alert('Введите слово');
		return false;
	}
	
	var i = 0;
	for(i; i < text_len; i++){
		var tsub = text.substr(i,text_len);
		if (slovo == tsub) {
			vivod.innerHTML = slovo;
		}
	}
	


}