HTML, CSS, and JavaScript are the most common front-end coding languages. The following table lists some online resources, references, and tutorials to help you continue practicing all three languages.
W3Schools: Reference guides for HTML, CSS, and JavaScript
HTML cheat sheet: Most commonly used HTML commands
CSS cheat sheet: Most commonly used CSS commands
HTML tutorials: Tutorials and articles for the web maintained by Google
CSS tutorials: Tutorials and articles for web programming, with a focus on CSS
JavaScript tutorials: Tutorials and reference guides for JavaScript