Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>Btn-group</title>
</head>
<body>

  <button>Join Group</button>

  <p></p>


  <div class="btn-group">
    <button>Join Group</button>
    <button>Leave Group</button>
  </div>

  <div class="btn-group">
    <button>Join Group</button>
    <button>Join Group</button>
    <button>Join Group</button>
  </div>

  <div class="btn-group">
    <button>Join Group</button>
    <button>Join Group</button>
    <button>Join Group</button>
    <button>Join Group</button>
  </div>

  </body>
</html>