<div id="root">
	<div class="title">This will not go fullscreen</div>
	<div id="fullscreen">
		<div class="title">This will go fullscreen</div>
		<button id="button">Toggle Fullscreen</button>
	</div>
</div>

button {
	border: none;
	padding: 8px 16px;
	background-color: #264653;
	color: white;
	cursor: pointer;
}

#root {
	position: relative;
	width: 1000px;
	font-size: 24px;
	height: 400px;
	background-color: #e9c46a;
	display: flex;
	flex-direction: column;
	justify-content: center;
	align-items: center;
}

#fullscreen {
	position: relative;
	width: 600px;
	height: 200px;
	display: flex;
	flex-direction: column;
	justify-content: center;
	align-items: center;
	background-color: #e76f51;
}

#fullscreen:fullscreen {
	/* 	background-color: yellow; */
}

#fullscreen::backdrop {
	background-color: transparent;
}

#root:fullscreen > #button {
	background-color: red;
	border: none;
}

.title {
	position: absolute;
	bottom: 40px;
	font-family: roboto;
	text-transform: uppercase;
	color: #264653;
}

body {
	height: 100vh;
	width: 100vw;
	background-color: #264653;
	margin: 0;
	box-sizing: border-box;
	display: flex;
	justify-content: center;
	align-items: center;
}

let fullscreen = document.querySelector("#fullscreen");
let button = document.querySelector("#button");

button.addEventListener("click", () => {
	if (!document.fullscreenElement) {
		fullscreen?.requestFullscreen();
	} else {
		document.exitFullscreen();
	}
});