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.com/css-media-resolution\n @media only screen and (min-resolution: 192dpi), // IE9-11 don't support dppx\n...