[4.0.x] Add CSS Variables for already implemented components

Problem/Motivation

6 components have been implemented as patterns:

• Block
• Box
• Button
• Content
• Notification
• Progress Bar

Title has been implement as UI Styles.

Only CSS Variables for Box and Block have been implemented.

Proposed resolution

Let's implement those for :

• Title
• Button
• Content
• Notification
• Progress Bar