<meta name="viewport" content="width=device-width, initial-scale=1">

<header>
	ini header
</header>

<section>
	<nav>
		ini nav
	</nav>

	<article>
		ini article
	</article>
</section>

<footer>
	ini footer
</footer>

<style>
	section {
  	display: flex;
	}

	nav {
  	flex: 1;
  	background: grey;
  	padding: 20px;
	}

	article {
  	flex: 3;
  	background: silver;
  	padding: 10px;
	}

       	@media (max-width: 600px) {
  	section {
    		flex-direction: column;
  		}
	}
</style>