It's all about the HTML. The following will load a stylesheet relative to the page you are currently on.
<link href="css/styles.css" rel="stylesheet">
For example, if your page is /products/page1.html. The browser will try to load /products/css/styles.css
An absolute path would look like:
<link href="/css/styles.css" rel="stylesheet">
Note the additional forward slash. In this case although your page is /products/page1.html. The browser will try to load /css/styles.css
You can also use the base tag to change the relative urls as in the first example.
<base href="/assets/" />
<link href="css/styles.css" rel="stylesheet">
This time the browser will try to load /assets/css/styles.css