Backport Bootstrap 4 spacing classes to Bootstrap 3 SASS/SCSS

_default-variables.scss

//== Spacing
//
$grid-breakpoints: (
  xs: 0,
  sm: $screen-sm-min,
  md: $screen-md-min,
  lg: $screen-lg-min
);
$spacer-x-0: 0rem;
$spacer-y-0: 0rem;
$spacer-x-1: .25rem;
$spacer-y-1: .25rem;
$spacer-x-2: .5rem;
$spacer-y-2: .5rem;
$spacer-x-3: 1rem;
$spacer-y-3: 1rem;
$spacer-x-4: 1.5rem;
$spacer-y-4: 1.5rem;
$spacer-x-5: 3rem;
$spacer-y-5: 3rem;
$spacers: (
  0: (
    x: $spacer-x-0,
    y: $spacer-y-0
  ),
  1: (
    x: $spacer-x-1,
    y: $spacer-y-1
  ),
  2: (
    x: $spacer-x-2,
    y: $spacer-y-2
  ),
  3: (
    x: $spacer-x-3,
    y: $spacer-y-3
  ),
  4: (
    x: $spacer-x-4,
    y: $spacer-y-4
  ),
  5: (
    x: $spacer-x-5,
    y: $spacer-y-5
  )
);

_spacing.scss

// https://github.com/entozoon/spacing-bootstrap-3 (original credit - experimetal repo)
//
// Porting from Bootstrap 4

// **************************** Ported mixins ********************************
@function breakpoint-min($name, $breakpoints: $grid-breakpoints) {
  $min: map-get($breakpoints, $name);
  @return if($min != 0, $min, null);
}
@mixin media-breakpoint-up($name, $breakpoints: $grid-breakpoints) {
  $min: breakpoint-min($name, $breakpoints);
  @if $min {
    @media (min-width: $min) {
      @content;
    }
  } @else {
    @content;
  }
}


//
// ****************************** _spacing.scss ******************************
// https://github.com/twbs/bootstrap/blob/v4-dev/scss/utilities/_spacing.scss

// Width and height

.w-100 { width: 100% !important; }
.h-100 { height: 100% !important; }

.mw-100 { max-width: 100% !important; }
.mh-100 { max-height: 100% !important; }

// Margin and Padding

.mx-auto {
  margin-right: auto !important;
  margin-left:  auto !important;
}

@each $breakpoint in map-keys($grid-breakpoints) {
  @each $prop, $abbrev in (margin: m, padding: p) {
    @each $size, $lengths in $spacers {
      $length-x:   map-get($lengths, x);
      $length-y:   map-get($lengths, y);

      @include media-breakpoint-up($breakpoint) {
        $min: breakpoint-min($breakpoint, $grid-breakpoints);

        @if $min {
          // everything else
          .#{$abbrev}-#{$breakpoint}-#{$size}  { #{$prop}:        $length-y $length-x !important; }
          .#{$abbrev}t-#{$breakpoint}-#{$size} { #{$prop}-top:    $length-y !important; }
          .#{$abbrev}r-#{$breakpoint}-#{$size} { #{$prop}-right:  $length-x !important; }
          .#{$abbrev}b-#{$breakpoint}-#{$size} { #{$prop}-bottom: $length-y !important; }
          .#{$abbrev}l-#{$breakpoint}-#{$size} { #{$prop}-left:   $length-x !important; }
          .#{$abbrev}x-#{$breakpoint}-#{$size} {
            #{$prop}-right:  $length-x !important;
            #{$prop}-left:   $length-x !important;
          }
          .#{$abbrev}y-#{$breakpoint}-#{$size} {
            #{$prop}-top:    $length-y !important;
            #{$prop}-bottom: $length-y !important;
          }
        } @else {
          // xs
          .#{$abbrev}-#{$size}  { #{$prop}:        $length-y $length-x !important; }
          .#{$abbrev}t-#{$size} { #{$prop}-top:    $length-y !important; }
          .#{$abbrev}r-#{$size} { #{$prop}-right:  $length-x !important; }
          .#{$abbrev}b-#{$size} { #{$prop}-bottom: $length-y !important; }
          .#{$abbrev}l-#{$size} { #{$prop}-left:   $length-x !important; }
          .#{$abbrev}x-#{$size} {
            #{$prop}-right:  $length-x !important;
            #{$prop}-left:   $length-x !important;
          }
          .#{$abbrev}y-#{$size} {
            #{$prop}-top:    $length-y !important;
            #{$prop}-bottom: $length-y !important;
          }
        }

      }
    }
  }
}

// Positioning

.pos-f-t {
  position: fixed;
  top: 0;
  right: 0;
  left: 0;
  z-index: $zindex-navbar-fixed;
}