zotero/scss/win/_menupopup.scss

menupopup, panel, #search-mode-popup {
	--panel-border-radius: 8px;
	--panel-background: var(--material-toolbar);
	--menuitem-hover-background-color: var(--fill-quinary);
	--menuitem-disabled-hover-background-color: var(--fill-quinary);
	@include light-dark(--panel-border-color, #dddddd, #1c1c1c);
}

menupopup {
	menu, menuitem {
		appearance: none !important;
		margin-left: 4px;
		margin-right: 4px;
		border-radius: 4px;
		fill: currentColor;
		-moz-context-properties: fill,fill-opacity;
		&[_moz-menuactive="true"] {
			background: var(--fill-quinary);
		}
	}
	menu {
		menupopup {
			padding-left: 6px;
			margin-top: -4px;
		}
	}
	menuseparator {
		margin: 4px 0px 4px 0px;
		border-top: var(--material-border50);
	}
}

.menu-accel {
	color: var(--fill-secondary);
	font-size: 11px;
}

.menu-iconic-left[disabled="true"] {
	opacity: 50%;
}

@media (-moz-windows-non-native-menus) {
	menuitem:is([checked="true"]):is([type="radio"]) > .menu-iconic-left {
		list-style-image: url("chrome://zotero/skin/win/menu-radio.svg");
	}

	menulist {
		menupopup {
			menu, menuitem {
				.menu-iconic-left {
					display: flex;
				}
			}

			menu:not([icon], .menu-iconic),
			menuitem:not([checked="true"], [icon], .menuitem-iconic) {
				padding-inline-start: 36px;

				.menu-iconic-icon {
					display: none;
				}
			}

			menuitem[selected="true"] {
				padding-inline-start: 12px !important;
		
				& > .menu-iconic-left {
					-moz-context-properties: fill, fill-opacity;
					fill: currentColor;
					fill-opacity: var(--menu-icon-opacity);
					list-style-image: url("chrome://zotero/skin/win/menu-radio.svg");
					width: 16px;
					margin-inline-end: 8px;
		
					& > .menu-iconic-icon {
						display: initial;
					}
				}
			}
		}
	}
}