CSS combinator

A CSS combinator specifies a structural relationship between parts of a CSS selector. A descendant space permits any depth, > requires an immediate child, + requires the next element sibling, and ~ permits a later element sibling. These operators determine which elements match; they contribute no CSS specificity of their own.^[ref]

Consider <section><h2>Title</h2><p>A</p><div><p>B</p></div><p>C</p></section>. The selector section p matches all three paragraphs. section > p matches A and C, since B has the div as its immediate parent. h2 + p matches A, the next element sibling of the heading. h2 ~ p matches A and C, the paragraph siblings following that heading.

Whitespace text between tags does not count as an intervening element sibling for the + relation. Likewise, ~ stays within one parent; it does not search arbitrarily far through the document for any later paragraph. This makes the distinction between document order and sibling relationships concrete.

A change in a combinator can therefore change a rule's scope without changing its selector counts. article p.warning and article > p.warning have the same CSS specificity but can match different paragraphs. Debugging a style rule requires checking the relationship it requests as well as the priority of the declarations it contains.