zotero/scss/components/_tabBar.scss

#tab-bar-container {
	// These variables can be overridden in platform styles to set platform-specific safe areas
	--safe-area-start: 0;
	--safe-area-end: 0;
	--tab-border: .5px solid var(--tab-border);

	min-height: 30px;
	
	&:not([hidden]) {
		// display: flex overrides the hidden attribute
		display: flex;
	}

	&::before {
		content: '';
		min-width: var(--safe-area-start);
		// Add bottom border to safe area space
		border-bottom: var(--tab-border);
	}

	&::after {
		content: '';
		min-width: var(--safe-area-end);
		// Add bottom border to safe area space
		border-bottom: var(--tab-border);
	}
	
	& > div {
		flex-grow: 1;
	}
}

.tab-bar-inner-container {
	display: flex;

	.tabs-wrapper {
		position: relative;
		flex-grow: 1;
	}

	.scroll-start-arrow, .scroll-end-arrow {
		height: 30px;
		padding: 0 3px;
		align-items: center;
		z-index: 1;
		color: var(--fill-tertiary);
		display: none;
		box-shadow: none;
		// Add bottom border to scroll arrows,
		// and negate the extra vertical pixel added by the border with a negative margin
		border-bottom: var(--tab-border);
		margin-bottom: -1px;
		box-sizing: border-box;

		.icon {
			display: flex;
		}

		&.active {
			color: var(--fill-secondary);
			&:hover {
				background-color: var(--fill-quinary);
			}
		}
	}

	.scroll-start-arrow {
		border-right: var(--material-border-transparent);
		&.active {
			border-right: var(--material-panedivider);
			box-shadow: 3px 0 3px -3px rgba(0, 0, 0, .3);
		}
	}

	.scroll-end-arrow {
		border-left: var(--material-border-transparent);
		&.active {
			border-left: var(--material-panedivider);
			box-shadow: -3px 0 3px -3px rgba(0, 0, 0, .3)
		}
	}

	.pinned-tabs {
		display: none;
		.tab {
			max-width: 110px;
		}
	}

	&.scrollable {
		.tabs-wrapper > .tabs > :first-child {
			display: none;
		}

		.scroll-start-arrow, .scroll-end-arrow {
			display: flex;
		}

		.pinned-tabs {
			display: block;
		}
	}
}

.tabs {
	display: flex;
	position: absolute;
	overflow: hidden;
	left: 0;
	right: 0;

	&:before {
		content: "";
		width: 0;
		min-width: 0;
		border-inline-end: var(--tab-border);
	}

	&:after {
		content: "";
		flex: 1 0 0;
		width: 100%;
		min-width: 0;
		// Add bottom border to the space between the last tab and the spacer in #tab-bar-container::after
		border-bottom: var(--tab-border);
		border-inline-start: var(--tab-border);
	}
}

.tab {
	box-sizing: border-box;
	-moz-appearance: none;
	max-width: 200px;
	flex: 1 1 200px;
	height: 30px;
	line-height: 30px;
	position: relative;
	color: var(--fill-primary);
	text-align: center;
	padding: 0 22px;
	min-width: 110px;
	
	&:not(:last-child) {
		border-inline-end: var(--tab-border);
	}
	
	&.selected {
		background: var(--material-button);
		box-shadow: 0px 0px 0px 0.5px rgba(0, 0, 0, 0.05), 0px 0.5px 2.5px 0px rgba(0, 0, 0, 0.30);
	}
	
	&.dragging {
		border-inline-start: var(--tab-border);
		z-index: 1;
	}
	
	&.dragging + & {
		border-inline-start: var(--tab-border);
	}
	
	.tab-name {
		line-height: 30px;
		overflow-x: hidden;
		text-overflow: ellipsis;
		display: -moz-box;
		-moz-box-pack: center;
		position: relative;
		top: -2px;
		overflow-y: hidden;

		.icon-bg {
			margin-inline-end: 7px;
			margin-top: -2px;
		}
	}

	.tab-close {
		position: absolute;

		&:dir(ltr) {
			right: 6px;
		}

		&:dir(rtl) {
			left: 6px;
		}

		top: 6px;
		width: 16px;
		height: 16px;
		text-align: center;
		line-height: 16px;
		border-radius: 3px;

		.icon {
			display: flex;
		}
		
		&:hover {
			background-color: var(--fill-quinary);
		}
		
		&:active {
			background-color: var(--fill-quarternary);
		}
	}

	&:first-child .tab-close {
		display: none;
	}

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