mastodon/app/javascript/styles/_mixins.scss

@mixin avatar-radius() {
  border-radius: $ui-avatar-border-size;
  background: transparent no-repeat;
  background-position: 50%;
  background-clip: padding-box;
}

@mixin avatar-size($size:48px) {
  width: $size;
  height: $size;
  background-size: $size $size;
}

@mixin single-column($media, $parent: '&') {
  .auto-columns #{$parent} {
    @media #{$media} {
      @content;
    }
  }
  .single-column #{$parent} {
    @content;
  }
}

@mixin multi-columns($media, $parent: '&') {
  .auto-columns #{$parent} {
    @media #{$media} {
      @content;
    }
  }
  .multi-columns #{$parent} {
    @content;
  }
}