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

/* Popovers/Menus */

// the popover itself
.popup-menu-boxpointer {
  -arrow-border-radius: $modal_radius;
  -arrow-background-color: $bg_color;
  -arrow-border-color: $borders_color;
  -arrow-border-width: 1px;
  -arrow-base: 24px;
  -arrow-rise: 12px; 
  -arrow-box-shadow: none; // dreaming bugzilla #689995
  margin: $base_margin; // used as distance from the 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 {
    -boxpointer-gap: $base_margin+2px; // distance from the panel
    
    // override popover styles for panel menus so
    // we can draw a box shadow and no arrow
    -arrow-border-radius: $modal_radius;
    -arrow-background-color: transparent;
    -arrow-border-color: transparent;
    -arrow-border-width: 0;
    -arrow-base: 0;
    -arrow-rise: $base_margin; // use this as top margin
    -arrow-box-shadow: none; // dreaming bugzilla #689995
    
    margin-bottom: 1.75em; // so it doesn't touch the bottom of the screen

    // style the menu content instead
    .popup-menu-content {
      border-radius: $modal_radius;
      border: 1px solid $borders_color; 
      box-shadow: 0 2px 4px 0 rgba(0,0,0,0.1);
      background-color: $bg_color;
      padding: $base_padding * 2;
    }

    .popup-menu-item {}
  }
}

// popover content;
.popup-menu-content {
  padding: $base_padding;
}

// menu items
.popup-menu-item {
  spacing: $base_spacing;
  padding: $base_padding*2;
  margin: 2px 0;
  border-radius: $base_border_radius;
  transition: 0.2s all ease;

  &:ltr { padding-right:1.75em; padding-left: 0; }
  &:rtl { padding-right: 0; padding-left:1.75em; }

  &:hover {
    background-color: $hover_bg_color;
  }

  &:checked {
    background-color: $hover_bg_color;
    font-weight: bold;

    margin-bottom: 0;
    box-shadow: inset 0 -1px 0 0 darken($hover_bg_color, 5%);
    border-radius: $base_border_radius $base_border_radius 0 0;
    
    &:hover {
      background-color: darken($hover_bg_color, 4%);
    }
  }

  &.selected {
    background-color: transparentize($fg_color, if($variant=='light', 0.7, 0.9));
    color: $fg_color;
  }

  &:active { 
    background-color: $active_bg_color;
    color: $active_fg_color;
  }

  &:insensitive { color: transparentize($fg_color,0.5);}
}

// all icons and other graphical elements
.popup-inactive-menu-item {
  color: $fg_color;

  // "Open Windows" label
  font-weight: bold;
  font-size: smaller;

  &:insensitive { color: $insensitive_fg_color; }
}

// symbolic icons in popover
.popup-menu-arrow,
.popup-menu-icon { 
  margin: 0;
  padding:0;
  icon-size: 16px !important;
}

.popup-menu-arrow {
  margin-right: $base_margin;
}

// popover submenus
.popup-sub-menu {
  background-color: $hover_bg_color;
  border:none;
  border-radius: 0 0 $base_border_radius $base_border_radius;
  padding: 0;
  margin-top: 0;
  &:active {
    background-color: transparent;
  }

  
  
  .popup-menu-ornament {
    min-width: 14px !important;
  }

  .popup-menu-item {
    margin: 0;
    border-radius: 0;
    padding: $base_padding*1.5 $base_padding*2;

    &:last-child:hover{
      border-radius: 0 0 $base_border_radius $base_border_radius;
    }
  }

  .popup-separator-menu-item {
    margin: 0;
  }
}

// container for radio and check boxes
.popup-menu-ornament {
  width: 1.2em;
  font-weight: bold;
  font-size: 1em;

  &:ltr { text-align: right; };
  &:rtl { text-align: left; };
}

// separator
.popup-separator-menu-item {
  padding: 0;

  .popup-separator-menu-item-separator {
    //-margin-horizontal: 24px;
    height: 1px; //not really the whole box
    margin: $base_margin 4em;
    background-color: lighten($borders_color, 2%);

    .popup-sub-menu & { //submenu separators
      margin: 0 4em 0 3em; // balance it in the middle
      padding:0 !important;
      background-color: darken($hover_bg_color, 5%);
    }
  }
}

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

// system status menu
.aggregate-menu {
  min-width: 21em;

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

  .popup-menu-item {
    &:ltr { padding-left:$base_padding;padding-right:$base_padding*2; }
    &:rtl { padding-right:$base_padding;padding-left:$base_padding*2; }
  }

  // lock screen, shutdown, etc. buttons
  .popup-menu-icon { 
    padding:0;
    margin: 0 $base_margin;
    -st-icon-style: symbolic;
  }

  .popup-sub-menu .popup-menu-item > :first-child {
    // account for icons in submenus with padding
    &:ltr {
      padding-left: 0;
      margin-left: $base_icon_size;
    }
    &:rtl {
      padding-right: 0;
      margin-right: $base_icon_size;
    }
  }
}