<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .parent {
            width: 100px; height: 100px;
            background: red;
            border-radius: 5px;
        }

        .child {
            width: 50px; height: 50px;
            background: green;
        }
    </style>
</head>
<body>
<div class="parent">
    <div class="child"></div>
</div>
<script>
    document.querySelector('.child').addEventListener('click', function() {
        alert('it works')
    })
</script>
</body>
</html>