<article>
	<section>foo</section>
	<aside>
		
		<p>piyo</p>
		<p>piyo</p>
		<p>piyo</p>
		<p>piyo</p>
		<p>piyo</p>
		<p>piyo</p>
		<h3>bar</h3>
		<h4>hoge</h4>
		<p>piyo</p>
		<p>piyo</p>
		<p>piyo</p>
		<p>piyo</p>
	</aside>
</article>
article {
	width: 100%;
	background: #ffeb3b;
	display: flex;
	justify-content: space-between;
	height: 2000px;
}

section {
	width: 75%;
	background: #f44336;
}

aside {
	width: 25%;
	background: #2196f3;
}

aside h3 {
	background: yellow;
	position: -webkit-sticky;
	position: sticky;
	top: 0;
}

External CSS

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External JavaScript

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