zotero/scss/mac/_tabBar.scss

.tabs {
	-moz-window-dragging: drag;
}

.tabs-spacer-before {
	width: 78px;
	border-bottom: $tab-border;
	border-inline-end: $tab-border;
}

.tabs-spacer-after {
	flex: 1;
	border-inline-start: $tab-border;
	border-bottom: $tab-border;
}

.tab {
	-moz-window-dragging: no-drag;
}

.tab:not(.selected) {
	border-bottom: $tab-border;
}

.tab:first-child {
	border-left: 0;
}

.tab:last-child {
	border-right: 0;
}