Untitled

<!DOCTYPE HTML>
<html>
<head>
    <meta charset="utf-8">
    <title>length</title>
</head>
<body>
<div id="elem"><p>text</p></div>
<button class="btn">Кликни сюда</button>
<script>
    let p = document.querySelector('#elem');
    let button = document.querySelector('.btn');

    button.addEventListener('click', function() {
        elem.style.padding = '30px';
        elem.style.color  = 'green';
    });

</script>
</body>
</html>