回答

很多种方式

一、在线工具

https://uncss-online.com/

二、命令行中

npm install -g uncss

Usage: uncss [options] <file or URL, ...>
    e.g. uncss https://getbootstrap.com/docs/3.3/examples/jumbotron/ > stylesheet.css

Options:

  -h, --help                            output usage information
  -V, --version                         output the version number
  -i, --ignore <selector, ...>          Do not remove given selectors
  -m, --media <media_query, ...>        Process additional media queries
  -C, --csspath <path>                  Relative path where the CSS files are located
  -s, --stylesheets <file, ...>         Specify additional stylesheets to process
  -S, --ignoreSheets <selector, ...>    Do not include specified stylesheets
  -r, --raw <string>                    Pass in a raw string of CSS
  -t, --timeout <milliseconds>          Wait for JS evaluation
  -H, --htmlroot <folder>               Absolute paths' root location
  -u, --uncssrc <file>                  Load these options from <file>
  -n, --noBanner                        Disable banner
  -a, --userAgent <string>              Use a custom user agent string
  -I, --inject <file>                   Path to javascript file to be executed before uncss runs
  -o, --output <file>                   Path to write resulting CSS to