preprocessor to embed .css files into .html files [on hold]

I'm looking for a tool that will embed link CSS files into the .html file.

This tool would scan the .html file. It would replace a line like:

<link rel="stylesheet" href="main.css" type="text/css" />

with the contents of the file main.css (wrapped in a <style> element). It would re-write the .html file with the embedded CSS code.

I have found tools that "inline" the CSS within HTML elements (<div style="...">). These are intended for email.
However, I want a tool that would embed the linked CSS code in a <style> element.