<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title></title>
<link rel="stylesheet" href="">
</head>
<body>
<button style="background-color:skyblue;">
Click me
</button>
<script>
let btn = document.querySelector('button');
btn.addEventListener('click',showMsg);
function showMsg(){
alert("Hello");
}
</script>
</body>
</html>