wordpress/wp-includes/css/customize-preview.css

.customize-partial-refreshing {
	opacity: 0.25;
	transition: opacity 0.25s;
	cursor: progress;
}

/* Override highlight when refreshing */
.customize-partial-refreshing.widget-customizer-highlighted-widget {
	box-shadow: none;
}

/* Make shortcut buttons essentially invisible */
.widget .customize-partial-edit-shortcut,
.customize-partial-edit-shortcut {
	position: absolute;
	float: left;
	width: 1px; /* required to have a size to be focusable in Safari */
	height: 1px;
	padding: 0;
	margin: -1px 0 0 -1px;
	border: 0;
	background: transparent;
	color: transparent;
	box-shadow: none;
	outline: none;
	z-index: 5;
}

/**
 * Styles for the actual shortcut
 *
 * Note that some properties are overly verbose to prevent theme interference.
 */
.widget .customize-partial-edit-shortcut button,
.customize-partial-edit-shortcut button {
	position: absolute;
	left: -30px;
	top: 2px;
	color: #fff;
	width: 30px;
	height: 30px;
	min-width: 30px;
	min-height: 30px;
	line-height: 1 !important;
	font-size: 18px;
	z-index: 5;
	background: #3858e9;
	border-radius: 50%;
	border: 2px solid #fff;
	box-shadow: 0 2px 1px rgba(60, 67, 74, 0.15);
	text-align: center;
	cursor: pointer;
	box-sizing: border-box;
	padding: 3px;
	animation-fill-mode: both;
	animation-duration: .4s;
	opacity: 0;
	pointer-events: none;
	text-shadow:
		0 -1px 1px #135e96,
		1px 0 1px #135e96,
		0 1px 1px #135e96,
		-1px 0 1px #135e96;
}
.wp-custom-header .customize-partial-edit-shortcut button {
	left: 2px
}

.customize-partial-edit-shortcut button svg {
	fill: #fff;
	min-width: 20px;
	min-height: 20px;
	width: 20px;
	height: 20px;
	margin: auto;
}

.customize-partial-edit-shortcut button:hover {
	background: #2145e6 !important; /* matches primary buttons */
}

.customize-partial-edit-shortcut button:focus {
	box-shadow: 0 0 0 1.5px #3858e9;
}

body.customize-partial-edit-shortcuts-shown .customize-partial-edit-shortcut button {
	animation-name: customize-partial-edit-shortcut-bounce-appear;
	pointer-events: auto;
}
body.customize-partial-edit-shortcuts-hidden .customize-partial-edit-shortcut button {
	animation-name: customize-partial-edit-shortcut-bounce-disappear;
	pointer-events: none;
}

.page-sidebar-collapsed .customize-partial-edit-shortcut button,
.customize-partial-edit-shortcut-hidden .customize-partial-edit-shortcut button {
	visibility: hidden;
}

@keyframes customize-partial-edit-shortcut-bounce-appear {
	from, 20%, 40%, 60%, 80%, to {
		animation-timing-function: cubic-bezier(0.215, 0.610, 0.355, 1.000);
	}
	0% {
		opacity: 0;
		transform: scale3d(.3, .3, .3);
	}
	20% {
		transform: scale3d(1.1, 1.1, 1.1);
	}
	40% {
		transform: scale3d(.9, .9, .9);
	}
	60% {
		opacity: 1;
		transform: scale3d(1.03, 1.03, 1.03);
	}
	80% {
		transform: scale3d(.97, .97, .97);
	}
	to {
		opacity: 1;
		transform: scale3d(1, 1, 1);
	}
}

@keyframes customize-partial-edit-shortcut-bounce-disappear {
	from, 20%, 40%, 60%, 80%, to {
		animation-timing-function: cubic-bezier(0.215, 0.610, 0.355, 1.000);
	}
	0% {
		opacity: 1;
		transform: scale3d(1, 1, 1);
	}
	20% {
		transform: scale3d(.97, .97, .97);
	}
	40% {
		opacity: 1;
		transform: scale3d(1.03, 1.03, 1.03);
	}
	60% {
		transform: scale3d(.9, .9, .9);
	}
	80% {
		transform: scale3d(1.1, 1.1, 1.1);
	}
	to {
		opacity: 0;
		transform: scale3d(.3, .3, .3);
	}
}

@media screen and (max-width: 800px) {
	.widget .customize-partial-edit-shortcut button,
	.customize-partial-edit-shortcut button {
		left: -32px;
	}
}

@media screen and (max-width: 320px) {
	.widget .customize-partial-edit-shortcut button,
	.customize-partial-edit-shortcut button {
		left: -30px;
	}
}