Untitled

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Document</title>
        <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
        <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.5.3/dist/css/bootstrap.min.css" integrity="sha384-TX8t27EcRE3e/ihU7zmQxVncDAy5uIKz4rEkgIXeMed4M0jlfIDPvg6uqKI2xXr2" crossorigin="anonymous">
        <script>
            document.addEventListener('DOMContentLoaded', () => {
                let _btns = document.getElementsByTagName('button');
                for(item of _btns){
                    item.addEventListener('click', (e) => {
                        _btns[_btns.length-1].className = e.target.className;
                    });
                }
            });
        </script>
    </head>
    <body>
        <button class="btn btn-success d-block"> Click me</button>
        <button class="btn btn-danger d-block"> Click me</button>
        <button class="btn btn-info d-block btn-lg"> Click me</button>
        <button class="btn btn-warning d-block btn-sm"> Click me</button>
        <button class="btn btn-dark d-block"> Click me</button>
        <button> Click me</button>
    </body>
</html>