ex3_if.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h1><a href="#">WEB</a></h1>
    <input id="night_day" type="button" value="night" onclick="
    if(document.querySelector('#night_day').value === 'night'){
        document.querySelector('body').style.backgroundColor = 'black';
        document.querySelector('body').style.color = 'white';
        document.querySelector('#night_day').value = 'day';
    } else{
        document.querySelector('body').style.backgroundColor = 'white';
        document.querySelector('body').style.color = 'black';
        document.querySelector('#night_day').value = 'night';
    }
    ">
    <ol>
        <li><a href="#">HTML</a></li>
        <li><a href="#">CSS</a></li>
        <li><a href="#">JavaScript</a></li>
    </ol>
    <h2>JavaScript</h2>
    <p>
        Lorem ipsum dolor sit amet consectetur adipisicing elit. Sint distinctio earum praesentium, nulla, nihil quasi eius, expedita ipsum necessitatibus cum aliquid amet optio aliquam a soluta illum quia fugiat obcaecati.
    </p>
</body>
</html>