zotero/scss/components/_toolbar.scss

.toolbar {
	height: 41px !important; /* Hard-code this to fix toolbar icon compression on Linux */
	min-height: 41px; /* Needed to prevent squashing by stretched tag selector */
	margin: 0;
	padding: 0px 8px 0px 8px;
	min-width: 1px;
}

/* A decent hack: reverse the effective order of the dropmarker and icon in RTL
   mode so that the above CSS, which places the menubutton-start.png background
   on the toolbarbutton-icon, will make sense. (Otherwise the dropmarker appears
   outside the button.) Then just flip the entire thing horizontally! We want to
   do that anyway so that the Locate button will point to the left and Sync will
   rotate counter-clockwise.

   The other way to do this would be to set direction: ltr on buttons in the
   RTL toolbar, but that breaks popup positioning. */
#zotero-pane[dir=rtl] {
	.zotero-tb-button > .toolbarbutton-menu-dropmarker {
		-moz-box-ordinal-group: 0;
	}

	.zotero-tb-button > .toolbarbutton-icon {
		-moz-box-ordinal-group: 1;
	}

	.zotero-tb-button,
	.zotero-tb-button:first-child,
	.zotero-tb-button:last-child {
		transform: scaleX(-1);
	}

	@media not (-moz-platform: macos) {
		.zotero-tb-button > .toolbarbutton-icon {
			transform: scaleX(-1);
		}
	}
}

.zotero-toolbar {
	-moz-appearance: none;
	@media (-moz-platform: macos) {
		-moz-window-dragging: drag;
	}
	@media not (-moz-platform: macos) {
		-moz-window-dragging: no-drag;
	}

	@include macOS-inactive-opacity;
}

#zotero-layout-switcher .zotero-toolbar {
	background: var(--material-toolbar);
	border-bottom: var(--material-panedivider);
}

#zotero-collections-toolbar,
#zotero-items-toolbar,
#zotero-item-pane-header,
#zotero-tabs-toolbar {
	toolbarbutton {
		width: 28px;
		height: 28px;
		padding: 0px 4px 0px 4px;
		margin: 0px 4px 0px 4px;

		&[type="menu"] {
			min-width: 0;
			width: 40px;
		}

		&:focus-visible {
			outline: none;
			box-shadow: 0 0 0 var(--width-focus-border) var(--color-focus-border);
		}
	}

	&:first-child {
		margin-left: 0px;
	}

	&:last-child {
		margin-right: 0px;
	}
}

#zotero-collections-search {
	max-width: 0;
	transition: max-width 0.5s ease;
	padding: 0px 6px 0px 0px;
	margin: 0;
	appearance: none;
	visibility: hidden;
}

#zotero-collections-search.visible {
	max-width: 180px; 
	visibility: visible;
	/* Avoids flickering between pointer and text cursor during transition */
	cursor: text;
}

/* Hide collection search on pane collapse, otherwise it still shows when focused */
#zotero-collections-pane[collapsed=true] #zotero-collections-search.visible {
	visibility: hidden;
}

/* Hide the add button on pane collapse. Otherwise, it may show on top of 'New Item' */
#zotero-collections-pane[collapsed=true] #zotero-tb-collection-add {
	visibility: hidden;
}

.zotero-tb-button {
	-moz-user-focus: normal;
}