Reading the HTML in the MDN

• Content categories;
• Permitted content;
• Tag omission: if the start or end tag can be omit;
• Permitted parents;
• Permitted ARIA roles;
• DOM interface;

Content categories

Question 1: What is the height of span?

<span style="font-size: 16px; line-height: 1">hello</span>

From Rules Between Block Elements And Inline Blocks, we can learn that you can't set any with/height/line-height css property to inline-element. So the height of span is depende on the default browser.