zotero/scss/components/_richlistbox.scss

richlistbox.theme-listbox {
	background: var(--material-background);
	border: var(--material-panedivider);
	// Prevent horizontal scrollbar on Windows
	overflow-x: hidden;

	richlistitem {
		--listitem-selectedBackground: var(--tag-gray);
		--listitem-selectedFocusCurrentBackground: var(--color-accent);
		--listitem-selectedTextColor: var(--color-accent-text);
		--listitem-selectedBorder: transparent;
		--listitem-selectedBottomBorder: transparent;
		--listitem-selectedCurrentBorder: transparent;
		--listitem-selectedFocusBorder: transparent;
		--listitem-selectedFocusBottomBorder: transparent;
		--listitem-selectedFocusCurrentBorder: transparent;
		--listitem-selectedFocusBackground: var(--color-accent);
		--listitem-selectedFocusColor: var(--accent-white);
		--listitem-selectedColor: var(--accent-white);
		--listitem-selectedFocusCurrentBottomBorder: transparent;
	}
}

richlistitem {
	padding: 0.2em 0.4em;
}

richlistitem,
richlistitem > *,
richlistitem label {
	// Prevent word cut-off with double-byte characters
	overflow: hidden;
	white-space: nowrap;
	text-overflow: ellipsis;
	width: 100%;
}

richlistcheckbox[selected=true] {
	background-color: -moz-cellhighlight;
	color: -moz-cellhighlighttext;	
}