gnome-shell/data/theme/gnome-shell-sass/widgets/_workspace-switcher.scss

/* Workspace Switcher */

$ws_indicator_height: $large_icon_size;
$ws_dot_active: $ws_indicator_height / 3;
$ws_dot_inactive: $ws_indicator_height / 6;

.workspace-switcher {
  @extend %osd_panel;
  margin-bottom: 4em;
  spacing: $base_padding * 2;
  padding: $base_padding * 2 $base_padding * 3;
}

.ws-switcher-indicator {
  background-color: transparentize($osd_fg_color,0.5);
  padding: $ws_dot_inactive / 2;
  margin: ($ws_indicator_height - $ws_dot_inactive) / 2;
  border-radius: $ws_indicator_height;

  &:active {
    background-color: $osd_fg_color;
    padding: $ws_dot_active / 2;
    margin: ($ws_indicator_height - $ws_dot_active) / 2;
  }
}