What describes block elements in CSS?

Block elements in CSS are fundamental components of web design, and they have specific characteristics that distinguish them from other types of elements. One of the defining traits of block elements is that they can contain both other block elements and inline elements. This capability allows for complex layouts to be created, where a block-level container can hold various content types, like paragraphs, headings, and inline images.

Block elements occupy the full width available to them by default, which facilitates the stacking of these elements vertically within their parent element. This stacking nature is essential for organizing content in a structured format on a web page. Because block elements can encompass inline elements (like anchor tags or spans), they serve as the primary building blocks for creating comprehensive layouts that combine different types of content.

In contrast, some attributes mentioned in other options do not apply to block elements. For instance, block elements do typically require a closing tag, unless they are self-closing elements, which are quite rare in HTML. Additionally, while block elements will take up the full width of their parent container, their size is not strictly based on "only as much space as necessary"; that describes inline elements more accurately. Lastly, block elements certainly can have specified widths and heights, allowing designers to create more controlled layouts