gnome-shell-dark-theme/gnome-shell-sass/widgets/_dash.scss

/* Dash */

// uses system colors
$dash_background_color: $system_overlay_bg_color;

$dash_placeholder_size: 32px;
$dash_padding: $base_padding * 2;
$dash_edge_offset: $base_margin * 3;
$dash_border_radius: $modal_radius + $dash_padding;
$dash_spacing: $base_margin * 0.5;

// container for the dash
#dash {
  // a bit of spacing so that dash doesn't touch the screen edges
  padding-left: $base_padding;
  padding-right: $base_padding;

  // background behind item container
  .dash-background {
    background-color: $dash_background_color;
    border-radius: $dash_border_radius;
    padding-top: $dash_padding;
    padding-bottom: $dash_padding;
    padding-left: $dash_padding - $dash_spacing; // subtract the margins added to .overview-tile below
    padding-right: $dash_padding - $dash_spacing;

    @if $contrast == 'high' {
      @include draw_hc_inset($width: 2px);
    }
  }

  // items on the dash
  .dash-item-container {

    .placeholder {
      // background-image: url("resource:///org/gnome/shell/theme/dash-placeholder.svg");
      background-image: none;
      background-size: contain;
      height: $dash_placeholder_size;
    }

    .empty-dash-drop-target {
      width: $dash_placeholder_size;
      height: $dash_placeholder_size;
    }

    // IMPORTANT: items on the dash need to extend to the edge to be adequate click targets
    // as such the %tile style is overriden and button styles are applied to the child class .overview-icon
    .show-apps,
    .overview-tile {
      // remove styles
      @extend %reset;

      margin: 0 $dash_spacing;
      padding-bottom: $dash_edge_offset; // align with other items

      $fg:$system_fg_color;
      $bg:$dash_background_color;

      .overview-icon {
        @extend %tile;
        @include button(normal, $tc:$fg, $c:$bg, $style: flat, $always_dark: true);
      }

      &:focus .overview-icon { @include button(focus, $tc:$fg, $c:$bg, $style: flat, $always_dark: true);}
      &:hover .overview-icon { @include button(hover, $tc:$fg, $c:$bg, $style: flat, $always_dark: true);}
      &:active .overview-icon { @include button(active, $tc:$fg, $c:$bg, $style: flat, $always_dark: true);}
      &:checked .overview-icon { @include button(checked, $tc:$fg, $c:$bg, $style: flat, $always_dark: true);}
    }

    // running app dot
    .app-grid-running-dot {
      // manually position the dot within the dash item
      @if $contrast == 'high' {
        offset-y: -$dash_padding - 1px; // don't draw dot directly on inset
      } @else {
        offset-y: -$dash_padding;
      }
    }
  }

  // separator between pinned and running apps
  .dash-separator {
    width: 1px;
    margin-left:$base_margin;
    margin-right:$base_margin;
    background-color: $system_borders_color;

    @if $contrast == 'high' {
      width: 2px;
      background-color: $hc_inset_color;
    }
  }

  // make sure all dash components have same margin from screen edge
  .dash-separator,
  .dash-background {
    margin-bottom: $dash_edge_offset;
  }
}

// OSD Tooltip
.dash-label {
  @extend %tooltip;
  -y-offset: $base_margin * 2; // distance from the dash edge
}