Content for User Experience, Design, & Graphical Flexibility

As a visitor I want to experience features for that area.

AC: At least one example are given for:

Web-based, designer-friendly style and template management for multiple templates, including base, sitewide, parent/child, and custom templates.
Multiple page types and themes styled through CSS for graphic flexibility and responsive design of all elements.
Enhance user experience by easily integrating existing and future progressive web apps.
Skinnable user interface for frontend users with dynamic graphical menus and multiple menu types.