zotero/scss/linux/_titleBar.scss

// Prevent window background overflows window border
#main-window {
	background-color: initial;
}

// Prevent background flicker
#browser {
	background: var(--material-tabbar);
}

#titlebar {
	height: var(--tab-min-height);
	-moz-box-pack: center;
	pointer-events: none;
	-moz-appearance: -moz-window-titlebar;
}

#zotero-title-bar {
	border-top: 1px solid var(--toolbar-field-border-color);
}

#toolbar-menubar {
	pointer-events: none;
	visibility: visible;
	// space for 30*30 icon
	margin: 0 8px;
	height: var(--tab-min-height);
	appearance: none;
	flex: 1;
}

#menubar-items {
	pointer-events: all;
}

#main-menubar {
	height: var(--tab-min-height);
}

.titlebar-buttonbox {
	pointer-events: all;
	margin: 0 10px;
}

.titlebar-button {
	position: static;
	// Fix KDE rendering bug
	z-index: 1;
}

.titlebar-icon-container {
	display: none;
}

// Following rules from https://searchfox.org/mozilla-central/source/browser/themes/linux/browser.css

/* The button box must appear on top of the navigator-toolbox in order for
 * click and hover mouse events to work properly for the button in the restored
 * window state. Otherwise, elements in the navigator-toolbox, like the menubar,
 * can swallow those events. */
.titlebar-buttonbox {
	z-index: 1;
	display: flex;
	align-items: center;
	height: var(--tab-min-height);
}

/* Render titlebar command buttons according to system config.
 * Use full scale icons here as the Gtk+ does. */
.titlebar-min {
	appearance: auto;
	-moz-default-appearance: -moz-window-button-minimize;
	order: env(-moz-gtk-csd-minimize-button-position);
}
.titlebar-max {
	appearance: auto;
	-moz-default-appearance: -moz-window-button-maximize;
	order: env(-moz-gtk-csd-maximize-button-position);
}
.titlebar-restore {
	appearance: auto;
	-moz-default-appearance: -moz-window-button-restore;
	order: env(-moz-gtk-csd-maximize-button-position);
}
.titlebar-close {
	appearance: auto;
	-moz-default-appearance: -moz-window-button-close;
	order: env(-moz-gtk-csd-close-button-position);
}

/* When using lightweight themes, use our own buttons since native ones might
 * assume a native background in order to be visible. */
.titlebar-button:-moz-lwtheme {
	appearance: none;
	border-radius: 100%;
}
.titlebar-button > .toolbarbutton-icon:-moz-lwtheme {
	padding: 6px;
	-moz-context-properties: stroke;
	stroke: currentColor;
}
.titlebar-min:-moz-lwtheme {
	list-style-image: url(chrome://browser/skin/window-controls/minimize.svg);
}
.titlebar-max:-moz-lwtheme {
	list-style-image: url(chrome://browser/skin/window-controls/maximize.svg);
}
.titlebar-restore:-moz-lwtheme {
	list-style-image: url(chrome://browser/skin/window-controls/restore.svg);
}
.titlebar-close:-moz-lwtheme {
	list-style-image: url(chrome://browser/skin/window-controls/close.svg);
}
.titlebar-button:-moz-lwtheme:hover {
	background-color: color-mix(in srgb, currentColor 12%, transparent);
}
.titlebar-button:-moz-lwtheme:hover:active {
	background-color: color-mix(in srgb, currentColor 20%, transparent);
}
.titlebar-close:-moz-lwtheme:hover {
	background-color: #d70022;
	color: white;
}
.titlebar-close:-moz-lwtheme:hover:active {
	background-color: #ff0039;
}

@media (not (-moz-gtk-csd-minimize-button)) {
	.titlebar-min {
	display: none;
	}
}
@media (not (-moz-gtk-csd-maximize-button)) {
	.titlebar-restore,
	.titlebar-max {
	display: none;
	}
}
@media (not (-moz-gtk-csd-close-button)) {
	.titlebar-close {
	display: none;
	}
}

@media (-moz-gtk-csd-reversed-placement) {
	.titlebar-buttonbox {
		order: -1;
		margin-right: 0;
	}
}