HTML and CSS code validation is important because it helps ensure that the code is written correctly and follows established standards. This helps ensure that the website will display correctly and consistently across different browsers and devices. Additionally, validation can also help identify and fix any potential accessibility issues, such as code that may not be compatible with assistive technologies like screen readers. Validating code can also help catch errors and bugs early on, which can save time and resources in the long run. Overall, validating code is a best practice that helps ensure the website is accessible, compatible, and maintainable.

You can validate HTML and CSS code at the following links:

• Markup validation service
• CSS validation service

If you’ve built to the public folder you can copy and paste the HTML or CSS files directly from there. The first thing to check would be index.html. For CSS you can copy the CSS file from the browser inspector -> Sources.

You can also validate functionality with:

• Google Search URL inspector
• Google test rich results