How to call a CSS file from the right place

[Rodrigo12]

I'm starting a project in PHP, and I want to structure my files properly from the start (unlike my last project, which had almost every file in a single directory). The problem is the following, which I will describe with an example:Take the following files: index.php, includes/header.php, and css/common.css. index.php 'includes' the header (as will many other php files). The header then calls common.css so that its html elements can be placed properly. common.css will also provide styling for general elements in index.php and other files.Notice that since the header is being included, when the header calls common.css, it does so from the location of the file calling it; in this case, index.php. But if I add, say, modules/friends.php and call the header with it, it will be looking for the CSS file in the wrong spot!Initially I tried to remedy this by using the actual path for when I call CSS files. However, my local machine and web server have a different layout of directories, and therefore I cannot simply call /var/www/whatever.Can anyone help me or redirect me to a place where this sort of thing is documented?Thanks,Paragon