MaxCSS is a simple plugin for Wordpress CMS. It's purpose is to expand Additional CSS functionality in the customize theme interface, adding a to-maximize CSS editor icon.
This plugin adds a to-maximize icon in the Additional CSS screen. The to-maximize icon is generated and positioned in a dynamic manner inside it's container. It is based on requestFullscreen native Javascript function and if it is supported by the browser then the user can add it's CSS rules, using CSS editor in fullscreen mode. The user can exit fullscreen mode by pressing ESC or clicking again on the maxCSS button.
Download plugin as a .zip from github repo (option: clone or download as .zip) and install it through the plugin installation steps in wordpress administrator interface. Alternatively you can search through wordpress.org directory with the keyword maxCSS.
A step by step tutorial is available in link
Visit the following link