@each $breakpoint in $breakpoints {

    $key   : nth($breakpoint, 1);
    $value : nth($breakpoint, 2);

    .visible-#{$key} {
        @media only screen and #{$value} {
            display: block !important;
        }
    }

    .hidden-#{$key} {
        @media only screen and #{$value} {
            display: none !important;
        }
    }

}