Front-End

• Learn SASS (Sass Guide)
• Learn SASS (Codecademy Pro)
• Flexbox Zombies (Sign up for a free account)
• Flexbox Froggy
• A11Y Style Guide
• A comprehensive guide to design systems

Back-End

• Thymeleaf Interactive Tutorial
• Spring.io Guides
  • Building a RESTful Web Service
  • Accessing Relational Data using JDBC with Spring
  • Building an Application with Spring Boot
• Add User Authentication to Your Spring Boot App in 15 Minutes
• 7 Tips for Writing Better Unit Tests in Java

Full-Stack

• What is a T-Shaped developer?