A service like criticalcss.com will not reduce the overall CSS, it rather identifies styles necessary for the first part of the page, copies them to an inline style tag, then moves the rest of the CSS down the page so it does not slow down the initial page load. In contrast, Speed Demon reduces the overall CSS for a page by removing all the linked stylesheet files and replacing them with a single, highly optimized, CSS file. It concatenates styles in the order of appearance, preserving the original cascade. The final optimized CSS is then minified, further reducing the overall size.