Why does `not (some-width: Xem)` media query never

Question

I'm trying to negate the max-device-width media query (the reason for this is I don't won't both (max-device-width: X) and (min-device-width: X) to fire if the device has precisely that width). Unfortunately, the not (min-or-max-some-width: X) media queries never fire.

Here's a small fiddle. I expect two yellow lines on the desktop and two red lines on mobile. What I get is only one yellow line on the desktop (the last one) and only one red line on mobile (the first one).

What am I doing wrong?

Answer 1

When Media Queries was first introduced, it required the not keyword to be followed by a media type in order for the media query to be valid. It seems strange, but that's just how the grammar was defined (see the media_query production).

This is now fixed in Media Queries level 4 (see the <media_not> production), so what you have should work as expected in browsers that conform to MQ4. However, none of the browsers that have begun shipping level 4 media features has implemented the new grammar yet.

In the meantime, you'll need to add a media type. If the media type is not important, use all:

not all and (max-device-width: X)

Updated fiddle