1. Block-level element: refers to being able to exist independently, and is separated by line breaks (such as a new line after the end of a paragraph). Commonly used block-level elements include: p, h1~h6, div, ul, etc.;
2. Inline element: refers to the existence of other block-level elements, which are displayed immediately between the connected elements without line breaking. Commonly used inline elements include: img, span, li, br, etc.;
3. Top-level element: including html, body, frameset, which is represented by Block-level element, which belongs to high-level block-level elements.