Css box model: from the outside to the inside, margin, border, padding, content.

Block elements are in the page, occupying one line, can be set wide and high, can hold block elements and inline elements.

Common block elements are div, p, h1-h6, ul, etc. Inline elements have no attributes of width or height, but they can be on the same line as other elements. Generally, they cannot contain block elements. The height of inline elements is generally determined by the font size inside the element, and the width is controlled by the length of the content.

Common inline elements are a, b, span, strong, em, etc.