paper-gtk-theme/Paper/gtk-3.20/widgets/_progress-bars.scss

/*****************
 * Progress bars *
 *****************/

GtkProgressBar,
.progressbar,
progressbar {
  
  @extend %scale_trough;

  // sizing
  &.horizontal {
    trough,
    .trough,
    progress { min-height: 4px; }
  }

  &.vertical {
    trough,
    .trough,
    progress { min-width: 4px; }
  }

  &.horizontal progress { margin: 0 -1px; } // the progress node is positioned after the trough border
  &.vertical progress { margin: -1px 0; }   // this moves it over it.


  // FIXME: insensitive state missing and some other state should be set probably
  font-size: smaller;
  color: transparentize($fg_color, 0.6);

  &:active {
    border-radius:0px;
    color: transparentize(black,0.5);
    background-color: $selected_bg_color;
    border-color: darken($selected_bg_color, 10%);

    &:backdrop {
      background-color: lighten($selected_bg_color, 10%);
      border-color: lighten(darken($selected_bg_color, 10%), 10%);
    }
  }

  &:backdrop {
    transition: $backdrop_transition;
  }

  .progressbar,
  progress {
    @extend %scale_highlight;

    border-radius: 0px;

    // default 2px
    &.left {
      border-top-left-radius: 0px;
      border-bottom-left-radius: 0px;
    }

    &.right {
      border-top-right-radius: 0px;
      border-bottom-right-radius: 0px;
    }

    &.top {
      border-top-right-radius: 0px;
      border-top-left-radius: 0px;
    }

    &.bottom {
      border-bottom-right-radius: 0px;
      border-bottom-left-radius: 0px;
    }
  }

  &:backdrop .progressbar { @extend %scale_highlight:backdrop; } // states not passed here as well
  &:backdrop progress { @extend %scale_highlight:backdrop; } // states not passed here as well

  &.osd { // progressbar.osd used for epiphany page loading progress
    min-width: 3px;
    min-height: 3px;
    background-color: transparent;

    .trough,
    trough {
      border-style: none;
      border-radius: 0;
      background-color: transparent;
      box-shadow: none;
    }

    .progressbar,
    progress {
      border-style: none;
      border-radius: 0;
    }
  }

  // In-Row

  row,
  .list-row {

    &:selected {
      border: 1px solid darken($selected_bg_color, 10%);
      color: transparentize(black,0.5);
      background-color: $selected_bg_color;
    }   
  }
}