$screen-xs: 480px !default;
$screen-xs-min: $screen-xs !default;
$screen-sm: 768px !default;
$screen-sm-min: $screen-sm !default;
$screen-md: 992px !default;
$screen-md-min: $screen-md !default;
$screen-lg: 1200px !default;
$screen-lg-min: $screen-lg !default;
$screen-xs-max: ($screen-sm-min - 1) !default;
$screen-sm-max: ($screen-md-min - 1) !default;
$screen-md-max: ($screen-lg-min - 1) !default;