Bootstrap/scss/mixins/_media-queries.scss

// Media query mixins for default breakpoints

@mixin media-xs() {
  @include media-breakpoint-max(xs) { @content }
}

@mixin media-sm() {
  @include media-breakpoint-min(sm) { @content }
}

@mixin media-sm-max() {
  @include media-breakpoint-only(sm) { @content }
}

@mixin media-md() {
  @include media-breakpoint-min(md) { @content }
}

@mixin media-md-max() {
  @include media-breakpoint-only(md) { @content }
}

@mixin media-lg() {
  @include media-breakpoint-min(lg) { @content }
}