@Macsurfcat: You won't see any changes because
Kindle Previewer can't simulate older (non-azw3/KF8) Kindles.
To test your media queries, you'll need to:
1. Generate a .mobi file with Kindle Previewer/KindleGen.
2. Split it into mobi7 and azw3 components using
Kindle Unpack or the
Kindle Unpack Calibre plugin.
3. Test the
mobi7 component with an eInk Kindle or a Kindle app.