Questions about main_page.tpl.php

[simplex]

I am a newbie to osCMax & php and am attempting to learn how to modify the CSS-fluid-1 template. I believe I am using the newest version of the software with BTS.

At present I have printed up the main_page.tpl.php and the .css files along with printouts of both the browser visual and html view of the opening page of the shopping cart so I can try to follow along and become familar with how everything works.

At this point, I have a few questions about main_page.tpl.php that I hope someone can help with.

1) What is:
<?php
if(isset($css_page_width))
{
echo 'div#pageFrame { width: ' . $css_page_width . 'px;}';
}
?>

2) Why isn't the informationBox styles not in the main_layout.css file and could it be?

3) Why are there 2 places for the coolMenu and which one is correct?

4) Where is "navTopFrame" in the CSS files? It's made reference to in <div class="navBarFrame" id-"navTopFrame" right above the 'breadcrumb' in main_page.tpl.php.


One other general question....
Can we use a .js file on a page?
I.E. <SCRIPT LANGUAGE="JavaScript" SRC="mopics.js"></SCRIPT>
instead of having the javascript inserted into the page itself?

Maybe too many ?'s at a time and if so, I apologize but I am thankful for any help given.