<header>
<h1>Header</h1>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" preserveAspectRatio="none">
<path d="M0,50 Q50,0 100,50"></path>
</svg>
</header>
<article>
<section>
<h2>Content</h2>
</section>
</article>

header {
	position: relative;
	height: 150px;
	background: #00bcd4;
	background-size: cover;
}
svg {
	position: absolute;
	bottom: -50px;
	width: 100%;
	height: 100px;
	fill: #80deea;
}
section {
	height: 150px;
	background: #80deea;
}
h1,h2 {
	font-size: 2em;
	margin: 0;
	padding: 1em 0;
	text-align: center;
	color: #ffffff;
}