twbs--bootstrap/scss/mixins/_media-queries.scss

// Media query mixins

@mixin media-xs() {
  @media (max-width: $screen-xs-max) { @content }
}

@mixin media-sm() {
  @media (min-width: $screen-sm-min) { @content }
}

@mixin media-sm-max() {
  @media (min-width: $screen-sm-min) and (max-width: $screen-sm-max) { @content }
}

@mixin media-md() {
  @media (min-width: $screen-md-min) { @content }
}

@mixin media-md-max() {
  @media (min-width: $screen-md-min) and (max-width: $screen-md-max) { @content }
}

@mixin media-lg() {
  @media (min-width: $screen-lg-min) { @content }
}