Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
OBSOLETE: This policy is obsolete and doesn't work after Microsoft Edge 132. The :--foo syntax for the CSS custom state feature is being changed to :state(foo) in Microsoft Edge in order to comply with changes that have been made in Firefox and Safari. This policy lets the deprecated syntax to be used until Stable 132. This deprecation might break some Microsoft Edge-only websites that use the deprecated :--foo syntax. If you enable this policy, the deprecated syntax will be enabled. If you disable this policy or don't set it, the deprecated syntax will be disabled.