[selectors-4] Fix typo: pseudo-eleent → pseudo-element (#8216)

Author: SpikyC

selectors-4/Overview.bs

@@ -2260,7 +2260,7 @@ The Activation Pseudo-class: '':active''</h3>
 	for example, while a hyperlink is being triggered.
 
 	In addition, the '':active'' pseudo-class applies
-	while any generated box of <em>any</em> element (or pseudo-eleent)
+	while any generated box of <em>any</em> element (or pseudo-element)
 	is being actively indicated by a pointing device (in the “down” state),
 	e.g. between the time the user presses the primary mouse button and releases it,
 	or while a finger is pressing on a touchscreen.