postal/app/assets/stylesheets/application/global/_mixins.scss

@mixin scrollbars($size: 6px, $thumb: #979ea6, $track: #efefef) {
  &::-webkit-scrollbar {
    height: $size; // Horizontal Scrollbars
    width: $size; // Vertical Scrollbars
  }

  &::-webkit-scrollbar-thumb {
    background: $thumb;
  }

  &::-webkit-scrollbar-track {
    background: $track;
  }
}