This will grow over time as I get more recommendations from trusted sources.

# Responsive Web Design

Paid:

• 7 Essential Books on Responsive Web Design You Do Not Want to Miss
• Practical Web Inclusion and Accessibility: A Comprehensive Guide to Access Needs
• Responsive Web Design

Free:

• Build a responsive website

# CSS / SASS

Paid:

• Modern CSS Design Systems
• Modern CSS Layouts

Free:

• Official SASS Guide