b) Accompany the object code with a copy of the GNU GPL and this license
   document.

  4. Combined Works.

  You may convey a Combined Work under terms of your choice that,
taken together, effectively do not restrict modification of the
portions of the Library contained in the Combined Work and reverse
engineering for debugging such modifications, if you also do each of
the following:

the img element.\n  height: auto;\n}\n\n\n// Retina image\n//\n// Short retina mixin for setting background-image and -size.\n\n@mixin img-retina($file-1x, $file-2x, $width-1x, $height-1x) {\n  background-image: url($file-1x);\n\n  // Autoprefixer takes care of adding -webkit-min-device-pixel-ratio and -o-min-device-pixel-ratio,\n  // but doesn't convert dppx=>dpi.\n  // There's no such thing as unprefixed min-device-pixel-ratio since it's nonstandard.\n  // Compatibility info: https://caniuse.co...