Simple CSS的作者是Tom Usborne,目前有90,000+个有效安装。已经Tested with 5.4.1版本的wordpress。
Description
Need to add some custom CSS to your site? Simple CSS gives you an awesome admin editor and a live preview editor in the Customizer so you can easily add your CSS.
Want your CSS to only apply on a specific page or post? Simple CSS adds a metabox which allows you to do just that.
Check out GeneratePress, our awesome WordPress theme! (http://wp101.net/themes/generatepress)
Features include:

Full featured admin CSS editor
Dark and light editor themes
CSS editor in the Customizer so you can live preview your changes
Metabox for page/post specific CSS