While most people think that HTML is superficial, it is indeed a complicated language with thosands of tricks up in its sleeve. Here, I listed some of the things I have read during my journey.
https://developer.mozilla.org/en-US/docs/Web/HTML
https://developer.mozilla.org/en-US/docs/Learn/HTML/Introduction_to_HTML
https://developer.mozilla.org/en-US/docs/Learn/HTML/Introduction_to_HTML/Getting_started
https://developer.mozilla.org/en-US/docs/Learn/HTML/Introduction_to_HTML/The_head_metadata_in_HTML
https://developer.mozilla.org/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks
https://developer.mozilla.org/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML
https://developer.mozilla.org/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals
https://developer.mozilla.org/en-US/docs/Learn/HTML/Tables
https://developer.mozilla.org/en-US/docs/Learn/HTML/Tables/Basics
https://developer.mozilla.org/en-US/docs/Learn/HTML/Tables/Advanced
https://css-tricks.com/complete-guide-table-element/
only html parts. until "Important Style Rules for Tables"
https://developer.mozilla.org/en-US/docs/Learn/Common_questions/What_is_a_URL
https://www.w3schools.com/tags/ref_urlencode.ASP
https://www.24a11y.com/2017/the-trials-and-tribulations-of-the-title-attribute/
https://developer.mozilla.org/en-US/docs/Web/HTML/Inline_elements
https://developer.mozilla.org/en-US/docs/Web/HTML/Block-level_elements
https://developer.mozilla.org/en-US/docs/Learn/HTML/Multimedia_and_embedding
https://developer.mozilla.org/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images
https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Content_categories
w3school.com/html
https://www.w3schools.com/html/html_forms.asp
https://developer.mozilla.org/en-US/docs/Web/HTML/Date_and_time_formats
https://developer.mozilla.org/en-US/docs/Web/HTML/Quirks_Mode_and_Standards_Mode
https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes
https://developer.mozilla.org/en-US/docs/Web/HTML/Link_types/preload
https://developer.mozilla.org/en-US/docs/Web/HTTP/Link_prefetching_FAQ
https://developer.mozilla.org/en-US/docs/Web/HTML/Element
https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes
https://developer.mozilla.org/en-US/docs/Web/Media/Formats
https://developer.mozilla.org/en-US/docs/Learn/Accessibility/What_is_accessibility
https://developer.mozilla.org/en-US/docs/Learn/Accessibility/HTML
https://developer.mozilla.org/en-US/docs/Learn/Accessibility/WAI-ARIA_basics
https://developer.mozilla.org/en-US/docs/Learn/Accessibility/Multimedia
https://developer.mozilla.org/en-US/docs/Learn/Accessibility/Multimedia
https://developer.mozilla.org/en-US/docs/Learn/Accessibility/Mobile
https://developer.mozilla.org/en-US/docs/Web/Accessibility/Understanding_WCAG
https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA
https://developer.mozilla.org/en-US/docs/Web/Accessibility/Cognitive_accessibility
https://developer.mozilla.org/en-US/docs/Web/Accessibility/
https://developer.mozilla.org/en-US/docs/Web/Accessibility/Seizure_disorders
https://developer.mozilla.org/en-US/docs/Tools/Accessibility_inspector
+ the A11Y tree
https://www.w3.org/WAI/standards-guidelines/
https://www.w3.org/WAI/standards-guidelines/wcag/
https://www.w3.org/WAI/standards-guidelines/wcag/glance/
+ the long edition
https://www.w3.org/WAI/standards-guidelines/aria/
https://www.w3.org/TR/wai-aria-1.1/
I studied the whole website