<!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>
    <style>
        h1{
            color: red;
            border-radius: 100%;
            border: 2px solid green;
        }
    </style>
</head>
<body>
    <h1>Welcome</h1>
    <button>Click me</button>

    <script>
        const btn = document.querySelector('button');
        btn.addEventListener('click', function (params) {
            alert('Welcome')
        })
    </script>
</body>
</html>