firefox-gnome-theme/theme/parts/controls.css

/* Controls */
/* Switchers, Checkboxes, etc. */

@namespace xul "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";

/* Switchers */
.protections-popup-tp-switch-box {
	padding: 0 !important;
	-moz-box-pack: start !important;
}
#protections-popup-tp-switch:not([enabled])[showdotindicator]::after {
	display: none !important;
}
#protections-popup-tp-switch {
	background: var(--gnome-trough-background) !important;
	border: 0 !important;
	border-radius: 24px !important;
	min-width: 48px !important;
	width: 48px !important;
	min-height: 26px !important;
	padding: 0 !important;
	position: relative !important;
	display: block !important;
	margin: 0 !important;
}
#protections-popup-tp-switch:hover {
	background-image: var(--gnome-trough-hover-background) !important;
}
#protections-popup-tp-switch::before {
	position: absolute !important;
	top: 2px;
	left: 2px;
	background: #fff !important;
	box-shadow: 0 2px 4px rgba(0, 0, 0, .2);
	border: 0 !important;
	border-radius: 24px !important;
	height: 22px !important;
	width: 22px !important;
	transition: left .2s ease;
	outline: 0 !important;
}
#protections-popup-tp-switch[enabled] {
	background: var(--gnome-accent-bg) !important;
	padding-inline-start: 24px !important;
}
#protections-popup-tp-switch[enabled]::before {
	background: #fff !important;
	left: 24px;
}