sapper-template/components/Nav.html

<nav>
	<ul>
		<li><a class='{segment === undefined ? "selected" : ""}' href='.'>home</a></li>
		<li><a class='{segment === "about" ? "selected" : ""}' href='about'>about</a></li>

		<!-- for the blog link, we're using rel=prefetch so that Sapper prefetches
		     the blog data when we hover over the link or tap it on a touchscreen -->
		<li><a rel=prefetch class='{segment === "blog" ? "selected" : ""}' href='blog'>blog</a></li>

		{#if $user}
			<li><span on:click="logout()">sign out</span></li>
		{:else}
			<li><a class='{segment === "login" ? "selected" : ""}' href='login'>log in</a></li>
			<li><a class='{segment === "signup" ? "selected" : ""}' href='signup'>sign up</a></li>
		{/if}

	</ul>
</nav>

<script>
	export default {
		methods: {
			logout() {
				this.store.get().logout()
			}
		}
	};
</script>

<style>
	nav {
		border-bottom: 1px solid rgba(170,30,30,0.1);
		font-weight: 300;
		padding: 0 1em;
	}

	ul {
		margin: 0;
		padding: 0;
	}

	/* clearfix */
	ul::after {
		content: '';
		display: block;
		clear: both;
	}

	li {
		display: block;
		float: left;
	}

	.selected {
		position: relative;
		display: inline-block;
	}

	.selected::after {
		position: absolute;
		content: '';
		width: calc(100% - 1em);
		height: 2px;
		background-color: rgb(170,30,30);
		display: block;
		bottom: -1px;
	}

	a, span {
		text-decoration: none;
		padding: 1em 0.5em;
		display: block;
		cursor: pointer;
	}
</style>