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HTML Guide for pseudo-element

CSS: Unknown pseudo-element or pseudo-class “::file-selector-button”.

css
pseudo-element
file-selector-button

The ::file-selector-button has not been recognized by the W3C Validator. This seems to be a bug in the W3C Validator, which has already been reported.

CSS: Unknown pseudo-element or pseudo-class “::ng-deep”.

css
pseudo-element
ng-deep
angular

The ::ng-deep CSS selector is often used in an Angular Component’s CSS to override the styles of a third-party component or a child component’s styles.

This CSS selector is now deprecated.