DropCSS is described as 'unused CSS cleaner; it takes your HTML and CSS as input and returns only the used CSS as output' and is an app in the Development category. There are five alternatives to DropCSS for Self-Hosted solutions and CSS. The best alternative is UnCSS, which is both free and Open Source. Other great apps like DropCSS are uCSS (Free, Open Source), Purgecss (Free, Open Source), Helium CSS (Free, Open Source) and PurifyCSS (Free, Open Source).
uCSS is made for crawling (large) websites to find unused CSS selectors. Features of uCSS include: • Find unused CSS selectors, given a HTML code base. • Find duplicate CSS selectors (also when no HTML is given). • Count matches for each rule.
What is Purgecss? When you are building a website, chances are that you are using a CSS framework like Bootstrap, Materializecss, Foundation, etc... But you will only use a small set of the framework and a lot of unused CSS styles will be included.