Problem with using CSS stylesheet.

Technical Details

Forum version : #phpBB3
Position : Founder
Concerned browser(s) : Google Chrome
Who the problem concerns : Yourself
Forum link : http://yuri-village.fengbb.com/

Description of problem

I saw the post in this forum, about how to personalize chatbox.
URL: CLICK HERE!
I decided to add these function to my chatbox in the forum so I followed the steps instructed.

But where should I paste the code in? ( I mean which position in the CSS stylesheet )

I need help...

Let's take an example, I want to "Add a message on login"

Code:

$(window).load(function() {
  var chatbox_script = function() {
    $('#chatbox_option_co').click(function(){
      $('#chatbox').addClass('recently-connected');
      setTimeout(function(){ $('#chatbox').removeClass('recently-connected') }, 60000)
    })
  };
  var s=document.createElement('script');s.text="("+chatbox_script.toString()+")();";$('object[data^="/chatbox/index.forum"],iframe[src^="/chatbox/index.forum"]').each(function(){try{$(this.contentDocument||this.contentWindow.document).find("#chatbox").closest("html").find("head").first().each(function(){this.appendChild(s.cloneNode(true))})}catch(a){}})
});

Code:

#chatbox.recently-connected:after {
  font-family: "trebuchet ms", serif;
  font-size: 1.5em; line-height:1.5em; font-weight: bold; color: #8BC34A;
  box-shadow:0 0 5px #AED581; display:block; background: #F1F8E9; margin:auto;
  width:80%; margin:1.5% auto; padding:1%; white-space: pre;
  content: "Welcome to the chatbox =D \a If you are alone, place a log on the fire.";
}

CLICK HERE!

What should I do to add this function to my chatbox?

The first  code is a JavaScript code:  AP > Modules > HTML/JavaScript > JacvaScript Management.

Thank you. I know what to do now ^^