Manage and live-preview theme-specific and plugin-specific Custom CSS in the Customizer.
Write custom CSS that stays specific to each theme; so you can easily switch themes without losing customizations. Includes a place for theme-specific CSS (which is stored with each theme) and a place for plugin-specific CSS (which is run on every theme).
This plugin is extremely simple; no validation is performed on the CSS added here and revision history is not saved (although it will be if/when Customizer setting revisions are added to core).
Please note that Modular Custom CSS requires WordPress 4.0 or higher.