2.2.4 [CSS-Level2-2009] Section 6.4, The cascade


The specification states:

 The user may be able to specify style information for a particular document. For example, the user may specify a file that contains a style sheet or the user agent may provide an interface that generates a user style sheet (or behaves as if it did).

EdgeHTML Mode (Microsoft Edge)

Microsoft Edge does not support user styles and does not provide a UI or other mechanism to specify a user stylesheet.