CSS, JS, File access with realpath(dirname(__FILE__))

I searched but did not find a definitive answer for my question.

What is the best practice to include .css, .js, and other files? How do I declare it in my configuration file. I tried :

define('CONST_ADMIN_JAVASCRIPT_LOCATION', 'jscript/');

This works but i think is most elegant to define like this in index.php:

define( 'ADMIN_ROOT', realpath(dirname(__FILE__))); 

And then the css directory :

define('CONST_ADMIN_CSS_LOCATION', ADMIN_ROOT.'templates/default/css/');

So if i try this then when including css, js, and other files then I get an error : 404 Not Found

<link href="/var/www/html/mysite/adminarea/templates/default/css/default_admin.css.php "    rel="stylesheet" type="text/css">

The file is there so I'm thinking the .htaccess file restriction must be the problem.

This is my .htaccess file:

RewriteEngine on
# HTTP OVER SSL
#RewriteCond %{HTTPS} !on
#RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

# Redirect non-www to www
#RewriteCond %{HTTP_HOST} !^www\.
#RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]

# Restricting direcotry listings
Options -Indexes

## RESTRICTING UPLOADS ONLY FOR IMAGE FILES
<Files ^(*.jpeg|*.jpg|*.png|*.gif)>
order deny,allow
deny from all
</Files>

So what is the best practice solution for this problem ?