userChrome.css

:root {
	--navbar-height: 48px;
	--wc-height: 16px;
	--wc-left-margin: 10px;
	--wc-red: hsl(-10, 90%, 60%);
	--wc-yellow: hsl(50, 90%, 60%);
	--wc-green: hsl(160, 90%, 40%);
	--sidebar-collapsed-width: var(--navbar-height);
	--sidebar-width: 250px;
	--transition-duration: 0.2s;
	--transition-ease: ease-out;
}

/* hide tabline */
#navigator-toolbox {
	-moz-window-dragging: drag;
}

#titlebar {
	appearance: none !important;
}

#TabsToolbar .toolbar-items {
	display: none !important;
}

#TabsToolbar.browser-toolbar {
	display: block !important;
	position: absolute;
	right: 0;
	top: calc((var(--navbar-height) - var(--wc-height)) / 2);
}

#nav-bar {
	margin-right: calc(var(--wc-height) * 6 + var(--wc-left-margin));
	padding: calc((var(--navbar-height) - 40px) / 2) 0;
}

#urlbar {
	--urlbar-toolbar-height: 40px !important;
	z-index: 200 !important;
}

#private-browsing-indicator-with-label {
	display: none !important;
}

.titlebar-button > .toolbarbutton-icon {
	visibility: hidden;
}

.titlebar-button {
	padding: 0 !important;
	height: var(--wc-height) !important;
	min-height: var(--wc-height) !important;
	width: var(--wc-height) !important;
	min-width: var(--wc-height) !important;
	border-radius: 50%;
	opacity: 0.7 !important;
}

.titlebar-button:hover {
	transform: scale(1.1);
	opacity: 1 !important;
	cursor: pointer;
}

.titlebar-buttonbox {
	display: flex;
	margin-right: var(--wc-height);
	gap: var(--wc-height);
}

.titlebar-close {
	background: var(--wc-red) !important;
}

.titlebar-min {
	background: var(--wc-yellow) !important;
}

.titlebar-max,
.titlebar-restore {
	background: var(--wc-green) !important;
}

/* hide sidebar header */
#sidebar-box[sidebarcommand='treestyletab_piro_sakura_ne_jp-sidebar-action']
	#sidebar-header {
	display: none;
}

#sidebar-box {
	z-index: 100 !important;
	position: relative !important;
	min-width: var(--sidebar-collapsed-width) !important;
	max-width: var(--sidebar-collapsed-width) !important;
}

/* inner width = expanded width & move inner to only show initial-width long section */
#sidebar-box #sidebar {
	min-width: var(--sidebar-width) !important;
	max-width: var(--sidebar-width) !important;
	width: var(--sidebar-width) !important;
	transform: translateX(
		calc(var(--sidebar-collapsed-width) - var(--sidebar-width))
	);
	transition: var(--transition-duration) var(--transition-ease);
}

#sidebar-box #sidebar:hover {
	transform: translateX(0) !important;
}

#sidebar-box[sidebarcommand='viewBookmarksSidebar'] #sidebar {
	transform: translateX(0) !important;
}