paper-gtk-theme/Paper/gtk-3.18/widgets/_level-bars.scss

/*************
 * Level Bar *
 *************/
GtkLevelBar,
.level-bar {

  -GtkLevelBar-min-block-width: 32px;
  -GtkLevelBar-min-block-height: 6px;
  padding: 2px;

  &.horizontal.indicator-discrete.fill-block { margin: 0 1px; }
  &.horizontal.discrete block { margin: 0 1px; }

  &.vertical.indicator-discrete.fill-block { margin: 1px 0; }
  &.vertical.discrete block { margin: 1px 0; }

  %fill-block,
  .fill-block {

    border-radius:3px;
    margin: 2px;
    background-color: transparentize(black, 0.9);
    border:1px solid;
    border-color: $borders_color;
    box-shadow: 0 1px 0 0 $bottom_highlight;

    &.low,
    &.level-low {
      background-color: $red;
      border:1px solid;
      border-color: if($variant == 'light', darken($red, 10%), $borders_color);
      box-shadow:inset 0 1px 0 0 $top_highlight;
    }

    &.high,
    &.level-high {
      background-color: $green;
      border:1px solid;
      border-color: if($variant == 'light', darken($green, 10%), $borders_color);
      box-shadow:inset 0 1px 0 0 $top_highlight;
    }

    &.full,
    &.level-full {
      background-color: $selected_bg_color;
      border:1px solid;
      border-color: if($variant == 'light', $selected_borders_color, $borders_color);
      box-shadow:inset 0 1px 0 0 $top_highlight;
    }

    &.empty,
    &.level-empty {
      background-color: transparentize(black, 0.9);
      border:1px solid;
      border-color: $borders_color;
      box-shadow: 0 1px 0 0 $bottom_highlight;
    }
  }

  // Trough
  &.horizontal,
  &.vertical {
    .trough {
      border:none;
      background-color:transparent;
      margin: 2px;
    }
  }


  // Vertical
  &.vertical {
    -GtkLevelBar-min-block-width: 6px;
    -GtkLevelBar-min-block-height: 32px;

    .fill-block {

      @extend %fill-block;

    }
  }
}