Is my approach to separating css files correct?

Question

css

There is a standard site. From the pages: home, contacts, service catalog (5-10), gallery, about the company, blog.
I write all styles in one custom.css file. As a result, when the site is completely ready, when loading each individual page, styles that are not on the page are loaded.

At a small scale, this is not critical, but when the site is large and has a lot of unique styles - here you inadvertently think about how much it will be right to add your own unique css files on each individual page, if there are unique styles?

But there is also an html tag . But shamans on the net once said that it is undesirable to use css styles in the HTML code of the site. Help determine the logic of actions. <style>