Switch to stylelint. (#23572)

scss/mixins/_image.scss

@@ -20,6 +20,7 @@
 //
 // Short retina mixin for setting background-image and -size.
 
+// stylelint-disable indentation, media-query-list-comma-newline-after
 @mixin img-retina($file-1x, $file-2x, $width-1x, $height-1x) {
   background-image: url($file-1x);
 
@@ -27,8 +28,7 @@
   // but doesn't convert dppx=>dpi.
   // There's no such thing as unprefixed min-device-pixel-ratio since it's nonstandard.
   // Compatibility info: https://caniuse.com/#feat=css-media-resolution
-  @media
-  only screen and (min-resolution: 192dpi), // IE9-11 don't support dppx
+  @media only screen and (min-resolution: 192dpi), // IE9-11 don't support dppx
   only screen and (min-resolution: 2dppx) { // Standardized
     background-image: url($file-2x);
     background-size: $width-1x $height-1x;