HTML

Free courses

• Codecademy - Learn HTML
• Minim - HTML for Absolute Beginners
• MDN - Learn HTML

Free courses in Polish

• Jak zacząć programować? - Podstawy HTML + CSS w dwie godziny - kurs krok po kroku!

HTML elements

• Web Dev Simplified - The New dialog HTML Element Changes Modals Forever
• Minim - When to Use Semantic HTML Elements Instead of Divs (part of the HTML for Absolute Beginners series)
• Web Dev Simplified - 5+ Must Know HTML Tags That Almost Nobody Knows
• HTML Reference - It features all elements and attributes

Best practices

• 11 HTML best practices for login & sign-up forms

Images

• Web Dev Simplified - How To Load Images Like A Pro

Be careful when using loading="lazy"

Source

Additional content

Additional content in Polish

• Bartosz Zagrodzki - Do you know all input types?