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$mobile-screen: 690px;
$tablet-screen: 995px;
$desktop-screen: 1440px;

$screen: "only screen";
$mobile: "only screen and (max-width:#{$mobile-screen})";
$tablet: "only screen and (min-width:#{$mobile-screen}) and (max-width: #{$tablet-screen})";
$desktop: "only screen and (min-width:#{$tablet-screen})";
$landscape: "only screen and (orientation: landscape)";
$portrait: "only screen and (orientation: portrait)";

@media (min-width:320px) { /* smartphones, portrait iPhone, portrait 480x320 phones (Android) */ }
@media (min-width:480px) { /* smartphones, Android phones, landscape iPhone */ }
@media (min-width:600px) { /* portrait tablets, portrait iPad, e-readers (Nook/Kindle), landscape 800x480 phones (Android) */ }
@media (min-width:801px) { /* tablet, landscape iPad, lo-res laptops ands desktops */ }
@media (min-width:1025px) { /* big landscape tablets, laptops, and desktops */ }
@media (min-width:1281px) { /* hi-res laptops and desktops */ }

@media (max-width: 2560px) { }
@media (min-width: 2048px) and (max-width: 2559px) { }
@media (min-width: 1536px) and (max-width: 2047px) { } 
@media (min-width: 1024px) and (max-width: 1535px) { } 
@media (min-width: 512px) and  (max-width: 1023px) { } 
@media (max-width: 511px) { }