gnome-shell/data/theme/gnome-shell-sass/widgets/_popovers.scss

/* Popovers/Menus */

$menu_bg_color: $bg_color;
$menuitem_bg_color: lighten($menu_bg_color, 4%);
$menuitem_border_radius: $base_border_radius*1.5;

$submenu_bg_color: lighten($menu_bg_color, 7%);

// the popover itself
.popup-menu-boxpointer {
  -arrow-rise: $base_margin+2px; // distance from the panel & screen edge
}

// container of the popover menu
.popup-menu {
  min-width: 15em;
  color: $fg_color;

  //.popup-status-menu-item {font-weight: normal;  color: pink;} //dunno what that is
  &.panel-menu {
    margin-bottom: 1.75em; // so it doesn't touch the bottom of the screen
  }
}

// popover content
.popup-menu-content {
  padding: $base_padding;
  background-color: $bg_color;
  border-radius: $modal_radius*1.25;
  border: 1px solid $outer_borders_color;
  box-shadow: 0 2px 4px 0 $shadow_color;
}

// menu items
.popup-menu-item {
  @include menuitem($bg:$menu_bg_color);

  border-radius: $menuitem_border_radius;

  &:checked {
    border-radius: $menuitem_border_radius $menuitem_border_radius 0 0 !important;

    @if $is_highcontrast {
      border: 1px solid $hc_inset_color;
      border-bottom-width:0;
    }
  }

  // add margin to switches in menu items
  .toggle-switch {
    &:ltr { margin-left: $base_margin;}
    &:rtl { margin-right: $base_margin;}
  }
}


// all other graphical elements (sliders)
.popup-inactive-menu-item {
  color: $fg_color;
  &:insensitive { color: $insensitive_fg_color; }
}

// symbolic icons in popover
.popup-menu-arrow,
.popup-menu-icon {
  icon-size: 16px !important; // for some reason the variable doesn't work here
}

// popover submenus
.popup-sub-menu {
  border-radius: 0 0 $menuitem_border_radius+1px $menuitem_border_radius+1px;
  margin-bottom: $base_padding;

  @if $is_highcontrast {
    border: 1px solid $hc_inset_color;
  }

  .popup-menu-ornament {
    icon-size: $base_icon_size !important;
    width: $base_icon_size;
  }

  // submenu specific styles
  .popup-menu-item {
    border-radius: 0;
    @include menuitem($bg:$submenu_bg_color, $flat:false);
    border-top-width:0;

    &:last-child {
      border-radius: 0 0 $menuitem_border_radius $menuitem_border_radius;
      border-bottom-width:0;
    }
  }

  .popup-menu-section {
    .popup-menu-item:last-child {
      &:hover,&:focus { border-radius: 0;}
    }
    &:last-child .popup-menu-item:last-child {
      border-radius: 0 0 $menuitem_border_radius $menuitem_border_radius;
    }
  }
}

// container for radio and check boxes
.popup-menu-ornament {
  icon-size: $base_icon_size !important;
  width: $base_icon_size;
}

// separator
.popup-separator-menu-item {
  border:none !important;

  .popup-separator-menu-item-separator {
    height: 1px; //not really the whole box
    background-color: $borders_color;
  }

  .popup-menu-ornament {
    width: 0 !important;
  }

  // separators in submenus
  .popup-sub-menu & {
    background-color: transparent;

    // account for ornament
    &:ltr { margin-right: 2.5em;}
    &:rtl { margin-left: 2.5em;}

    .popup-separator-menu-item-separator {
      background-color: $borders_color;
    }
  }
}

// desktop background menu
.background-menu {
  -boxpointer-gap: 0px;
  -arrow-rise: 0px; // hide the beak on the menu
}

// right-click (and panel) app menu
.app-menu {
  max-width: 27.25em;

  // this is unneeded at the top-level in this menu, hide it
  .popup-menu-ornament { width: 0 !important; }

  .popup-inactive-menu-item:first-child {
    // "Open Windows" label
    > StLabel {
      @extend %caption_heading;
      &:ltr {margin-right: $base_margin*2;}
      &:rtl {margin-left: $base_margin*2;}
    }
  }
}