style.css

/*reset*/
* {
	padding: 0;
	margin: 0;
}

/*css variables*/
:root {
	--thumbnail-width: 20px;
	--thumbnail-height: 3px;
	--shadow: rgba(0, 0, 0, .25);
}

html, body {
	height: 100%;
	position: relative;
}

body {
	background: #000;
}

#sections-wrapper {
	position: relative;
	overflow: hidden;
	height: 100vh;
	background: #000;
}

section {
	height: 100vh;
	font-size: 0;
	text-align: center;
	position: absolute;
	top: 0;
	left: 0;
	right: 0;
	bottom: 0;
}

.hide-bottom {
	transform: translateY(100%);
}

.hide-top {
	transform: translateY(-100%);
}

.segment {
	height: 100%;
	display: inline-block;
	overflow: hidden;
	position: relative;
	box-sizing: border-box;
}

.segment-inner {
	position: absolute;
	top: 0;
	background: no-repeat center center / cover; 
	height: 100%;
	width: 100vw;
}

.sections-control {
	text-align: center;
	font-size: 0;
	position: fixed;
	right: 25px;
	bottom: 25px;
	box-sizing: border-box;;
}

.section-thumbnail {
	width: var(--thumbnail-width);
	height: var(--thumbnail-height);
	display: block;
	margin-top: 4px;
	padding: 4px 0;
	position: relative;
	transition: .3s all ease;
	opacity: .5;
	cursor: pointer;
	transform-origin: right top;
}

.section-thumbnail:before {
	content: "";
	position: absolute;
	top: 50%;
	left: 0;
	right: 0;
	height: var(--thumbnail-height);
	top: 50%;
	margin-top: calc(var(--thumbnail-height)/2 * -1);
	background: #fff;
}

.section-thumbnail:hover {
	opacity: 1;
}

.section-thumbnail.active {
	transform: scaleX(2);
	opacity: 1;
}