one-dark/gtk-3.0/sass/ui/menu.scss

//
// Menus
//
menubar,
.menubar {
  -GtkWidget-window-dragging: true;
  padding: 0px;
  background-color: $header_bg;
  color: $header_fg;

  &:backdrop {
    color: transparentize($header_fg, 0.3);
    //background-color: opacify($header_bg_backdrop, 1);
  }

  > menuitem {
    padding: 6px 8px;
    border: solid transparent;
    border-width: 0;

    &:hover {
      //Seems like it :hover even with keyboard focus
      background-color: $menu_selected_bg_color;
      color: $fg_color;
    }
    &:disabled {
      color: transparentize($header_fg, 0.6);
      border-color: transparent;
    }

    > label:disabled {
      color: transparentize($header_fg, 0.45);
    }
  }
}

menu,
.menu {
  $_menu_bg: $bg_color;
  margin: 4px;
  padding: 0;
  border-radius: 0;
  background-color: $_menu_bg;
  border: 1px solid $borders_color;

  .csd & {
    padding: 4px 0px;
    border-radius: 2px;
    border: none;
  }

  separator,
  .csd & separator {
    margin: 2px 0;
    background-color: $separator_color;
  }

  // Firefox workaround
  .separator:not(label),
  .csd & .separator:not(label) {
    color: $_menu_bg;
  }
  // Firefox workaround end

  menuitem {
    min-height: 16px;
    min-width: 40px;
    padding: 5px;

    &:hover {
      color: $fg_color;
      background-color: $menu_selected_bg_color;
    }
    &:disabled {
      color: $insensitive_fg_color;
    }

    //submenu indicators
    arrow {
      min-height: 16px;
      min-width: 16px;

      &:dir(ltr) {
        -gtk-icon-source: -gtk-icontheme('pan-end-symbolic');
        margin-left: 10px;
      }
      &:dir(rtl) {
        -gtk-icon-source: -gtk-icontheme('pan-end-symbolic-rtl');
        margin-right: 10px;
      }
    }
    @at-root menuitem {
      accelerator {
        color: gtkalpha(currentColor, 0.55);
      }

      check,
      radio {
        min-height: 16px;
        min-width: 16px;
        &:dir(ltr) {
          margin-right: 6px;
          margin-left: 2px;
        }
        &:dir(rtl) {
          margin-left: 6px;
          margin-right: 2px;
        }
      }
    }
  }

  // overflow buttons
  > arrow {
    @include button(undecorated);
    min-width: 16px;
    min-height: 16px;
    padding: 4px;
    background-color: $_menu_bg;
    border-radius: 0;

    &.top {
      margin-top: -6px;
      border-bottom: 1px solid mix($fg_color, $base_color, 10%);
      -gtk-icon-source: -gtk-icontheme('pan-up-symbolic');
    }
    &.bottom {
      margin-bottom: -6px;
      border-top: 1px solid mix($fg_color, $base_color, 10%);
      -gtk-icon-source: -gtk-icontheme('pan-down-symbolic');
    }
    &:hover {
      background-color: mix($fg_color, $base_color, 10%);
    }
    &:disabled {
      color: transparent;
      background-color: transparent;
      border-color: transparent;
    }
  }
}

.csd .popup {
  border-radius: 2px;
}

//
// Popovers
//
popover,
popover.background {
  $_popover_bg: $bg_color;
  padding: 2px;
  // border: 1px solid darken($borders_color, 5%);
  border-radius: 3px;
  background-clip: border-box;
  background-color: $_popover_bg;

  box-shadow: 0 2px 6px 1px transparentize(black, 0.65);

  .csd &,
  & {
    border: 1px solid darken($borders_color, 5%);
  }

  & separator {
    background-color: $_popover_bg;
  }
  label.separator {
    @extend .dim-label;

    color: $fg_color;
  }

  > list,
  > .view,
  > toolbar {
    border-style: none;
    background-color: transparent;
  }

  &,
  .csd & {
    &.osd,
    &.magnifier {
      @extend %osd;
    }
    &.touch-selection {
      @extend .context-menu;
    }

    &.osd {
      @extend %osd;
    }
  }
}

//touch selection handlebars for the Popover.osd above
cursor-handle {
  background-color: transparent;
  background-image: none;
  box-shadow: none;
  border-style: none;
  &.top {
    -gtk-icon-source: -gtk-icontheme('selection-start-symbolic');
  }
  &.bottom {
    -gtk-icon-source: -gtk-icontheme('selection-end-symbolic');
  }
}