Firstchildnextsibling

Firstchildnextsibling is a CSS pseudo-class selector. It matches an element that is the first child of its parent and is also the next sibling of another specified element. This means the element must satisfy two conditions simultaneously: it must be the very first element within its parent container, and it must immediately follow a particular sibling element.

In practice, firstchildnextsibling is not a standard or recognized CSS pseudo-class. It appears to be a misunderstanding or a hypothetical combination of existing selectors. The standard CSS pseudo-class for selecting the first child of its parent is :first-child. The standard CSS pseudo-class for selecting an element that is the next sibling of another element is :nth-child(n+2), when combined with a preceding sibling selector, or more directly, by targeting the sibling itself after the first child.

If the intention was to select an element that is the first child *and* the next sibling of some other element, this cannot be achieved with a single, direct pseudo-class like "firstchildnextsibling". One would typically use a combination of selectors, such as a descendant combinator or adjacent sibling combinator, to achieve complex relationships between elements. For example, to style the element that is the first child of its parent and also immediately follows another element, one might use a selector like `previous-element + first-child`. However, this still doesn't directly align with the concept of "firstchildnextsibling". The standard CSS selectors provide powerful ways to target elements based on their position and relationship to other elements without needing such a composite pseudo-class.