PHP, CSS dynamic nr of stylesheets?

I am playing around with PHP, HTML and CSS...

I keep my header in a separate file and include it.
For now I have two stylesheets (just to make the basics reusable, and to see how it worked out).
One can be dynamically changed (by me naming it in each file)

So my header contains this:

<link rel="stylesheet", type="text/css", href="stylesheets/basicStylesheet" />
<link rel="stylesheet", type="text/css", href="stylesheets/<?php echo $css ?>" />

and each of my files start off with this:

<?php
$css='Stylesheet.css';
require_once("Header.php");
?>

Would it be possible (and would it make sense ) to make it possible to choose to have just one stylehseet or to add one, two, three etc at wish?

I.e. if I have one page that is distinctly different, can I somehow get the header code to work in such a way that I can add a third stylesheet? Or would that just be a waste of time / resources?

Am just trying to figure out if it best to have one large stylesheet with everything, or several small ones that one can add at choice.

Typically it is best to keep CSS in a single file because multiple requests are much slower for the user and search engines dock SEO ranking on that stuff too. If you want to write CSS targeting a specific page then just handle writing your selectors correctly. For example, you could have a container div in each page with an id specific to that page. Then start all your selectors referencing that id for that page.
#about-page .some-class {
.....
}

Much more advanced, but if you are wanting to neatly organize your CSS then you could look into something like LESS or SASS compilers which would let you create lots of .less/.sass files and all be compiled into 1 .css file (if you setup it up correctly).

Okai, thanks

I think I'll keep it simple for now but I'll make a note of the less / sass concept in case I get use for it later.

It's debatable as to whether you should put you're stylesheet links in the footer. The positive is it will no long be render blocking, the negatives you get FLOUT (Flash Of Unstyled Text)

If your server is configured for HTTP/2 I think you are better off breaking up stylesheets, concatenation is obsolete in that respect.

That being said I haven't done any web development for a couple of months now (taking a break) so my info may be abit rusty lol