Responsive SCSS Mixins

_responsive.scss

@mixin linear {
    @media screen and (max-width: 45em) {
        @content;
    }
}

@mixin mobile-landscape {
    @media screen and (max-width: 30em) {
        @content;
    }
}

@mixin mobile-portrait {
    @media screen and (max-width: 20em) {
        @content;
    }
}

@mixin tight {
    @media screen and (min-width: 30em) and (max-width: 60em) {
        @content;
    }
}

@mixin full {
    @media screen and (min-width: 62em) {
        @content;
    }
}

@mixin short {
    @media screen and (max-height: 30em) {
        @content;
    }
}

@mixin retina {
    @media only screen and (-webkit-min-device-pixel-ratio: 1.5),
           only screen and (min-device-pixel-ratio: 1.5) {
        @content;
    }
}