Why Does `input:not(:empty)` Not Work as Expected?

Unveiling the Mysteries of the :not(:empty) CSS Selector

When attempting to control the appearance of empty or non-empty input fields using the :not(:empty) CSS selector, many developers encounter unexpected behavior. This selector seems to function flawlessly with other combinations, but introduces anomalies once :not(:empty) is added to the mix.

The confusion stems from the unique nature of input elements. HTML defines void elements as those that "are empty by nature," including the tag. As a result, all void elements, regardless of their value attribute, are consistently considered empty by the :empty pseudo-class.

Furthermore, the Selectors specification explicitly states that :empty targets elements with no child nodes, including text content. Consequently, input fields, despite having a value, will always lack child nodes and, hence, match the :not(:empty) selector.

In summary, using input:not(:empty) in a proper HTML document will always fail to match anything. This limitation arises due to the inherent nature of void elements in HTML and the definition of the :empty pseudo-class in CSS Selectors.

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