The Appearance/Customise/Additional CSS option places the script inline in your main HTML file, after compressing and optionally compiling the LESS or SASS.

However, for a standard theme the wp_register_style and wp_enqueue_style functions just include the raw css file via the bog-standard link
mechanism. Googling shows me a number of plugins that will merge and minify multiple css files, but WordPress already has that functionality built-in, so is there any way to take advantage of it?

Read more here: Inlining stylesheets like "Additional CSS" does


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