firefox-gnome-theme/chrome/parts/csd.css

/* GNOME CSD styles for headerbar on Firefox [tabsintitlebar] */

@import "csd-fullscreen.css";
@import "csd-left-controls.css";
@namespace xul url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

/* Navbar position */
:root[tabsintitlebar] #nav-bar {
	padding-right: 7px !important;
	position: relative;
}
:root[tabsintitlebar] #toolbar-menubar:not([inactive=true]) {
	height: 30px !important;
	margin-bottom: 8px;
}
:root[tabsintitlebar] #titlebar {
	-moz-appearance: none !important;
}

/* Add window controls separator */
:root[tabsintitlebar] #nav-bar::after {
	content: "";
	position: absolute;
	right: 3px;
	top: 6px;
	height: 34px;
	border-right: 1px solid rgba(0, 0, 0, .1);
}

/* Move window buttons next to the header bar */
:root[tabsintitlebar] #titlebar .titlebar-buttonbox-container {
	position: absolute !important;	
	right: 0;
	top: 0;
	-moz-appearance: none !important;
}
:root[tabsintitlebar] #titlebar .titlebar-buttonbox {  
	background-image: var(--gnome-headerbar-bgimage) !important;
	border-bottom: var(--gnome-headerbar-border-bottom) !important;
	box-shadow: var(--gnome-headerbar-box-shadow);
	height: unset !important;
	padding-right: 3px;	
	-moz-appearance: none !important;
}
:root[tabsintitlebar] #titlebar .titlebar-buttonbox:-moz-window-inactive {
	background-image: var(--gnome-inactive-headerbar-bgimage) !important;
	border-bottom: var(--gnome-inactive-headerbar-border-bottom) !important;
	box-shadow: var(--gnome-inactive-headerbar-box-shadow) !important;
}

/* Window buttons */
:root[tabsintitlebar] #titlebar .titlebar-button {
	-moz-appearance: none !important;
	border: var(--gnome-headerbar-button-border) !important;
	border-color: transparent !important;
	border-radius: 3px !important;
	height: 34px;
	margin: 6px 3px !important;
	padding: 0 2px !important;
	transition: all .3s ease-out;
	width: 34px;
}
:root[tabsintitlebar] #titlebar .titlebar-button .toolbarbutton-icon {
	filter: invert(85%);
	width: 16px;
}
:root[tabsintitlebar] #titlebar:-moz-window-inactive .titlebar-button .toolbarbutton-icon {
	opacity: .7 !important;
}
:root[tabsintitlebar] #titlebar:not(:-moz-window-inactive) .titlebar-button:not([disabled]):hover {
	background-image: var(--gnome-headerbar-button-hover-bgimage);
	border: var(--gnome-headerbar-button-border) !important;
}
:root[tabsintitlebar] #titlebar:not(:-moz-window-inactive) .titlebar-button:not([disabled]):active {
	background-image: var(--gnome-headerbar-button-active-bgimage);
	box-shadow: var(--gnome-headerbar-button-active-box-shadow);
	border: var(--gnome-headerbar-button-border) !important;
}
:root[tabsintitlebar] #titlebar:not(:-moz-window-inactive) .titlebar-button[disabled] {
	background-color: var(--gnome-headerbar-button-disabled-bgcolor);
	box-shadow: var(--gnome-headerbar-button-disabled-box-shadow);
	border: var(--gnome-headerbar-button-border) !important;
}

:root[tabsintitlebar] #titlebar .titlebar-buttonbox .titlebar-close .toolbarbutton-icon {
	filter: var(--gnome-icons-hack-filter);
	list-style-image: url("moz-icon://stock/window-close-symbolic?size=dialog") !important;
}
:root[tabsintitlebar] #titlebar .titlebar-buttonbox .titlebar-max .toolbarbutton-icon {
	filter: var(--gnome-icons-hack-filter);
	list-style-image: url("moz-icon://stock/window-maximize-symbolic?size=dialog") !important;
}
:root[tabsintitlebar] #titlebar .titlebar-buttonbox .titlebar-min .toolbarbutton-icon {
	filter: var(--gnome-icons-hack-filter);
	list-style-image: url("moz-icon://stock/window-minimize-symbolic?size=dialog") !important;
}

/* Fix the issue when dragging tabs */
:root[tabsintitlebar] #navigator-toolbox[movingtab] #TabsToolbar {
	padding-bottom: 0 !important;
}

/* Window controls: at least 1 button */
@media (-moz-gtk-csd-minimize-button), (-moz-gtk-csd-maximize-button), (-moz-gtk-csd-close-button) {
	:root[tabsintitlebar] #nav-bar {
		margin-right: 43px;
	}
}
/* Window controls: at least 2 buttons */
@media (-moz-gtk-csd-minimize-button) and (-moz-gtk-csd-maximize-button),
       (-moz-gtk-csd-minimize-button) and (-moz-gtk-csd-close-button),
       (-moz-gtk-csd-maximize-button) and (-moz-gtk-csd-close-button) {
	:root[tabsintitlebar] #nav-bar {
		margin-right: 83px;
	}
}
/* Window controls: 3 buttons */
@media (-moz-gtk-csd-minimize-button) and (-moz-gtk-csd-maximize-button) and (-moz-gtk-csd-close-button) {
	:root[tabsintitlebar] #nav-bar {
		margin-right: 123px;
	}
}

/* CSD rounded corners */
:root[tabsintitlebar]:not([sizemode="maximized"]):not([inFullscreen]) #navigator-toolbox {
	border: 1px solid var(--gnome-window-border-color) !important;
	border-radius: 8px 8px 0 0 !important;
	margin: -1px -1px 0 -1px !important;
}
:root[tabsintitlebar]:not([sizemode="maximized"]):not([inFullscreen]) #nav-bar {
	border-top-left-radius: 8px;
}
:root[tabsintitlebar]:not([sizemode="maximized"]):not([inFullscreen]) .titlebar-buttonbox {
	border-top-right-radius: 8px;
}