JSFiddle - React, Tailwind, and code Playground

CSS

$default_color: #999;
$hover_color: #009ac8;
$header_back: #f7f7f2;
$aside_hover: #182383;
body {
	margin: 0;
	padding: 0;
}
nav {
	ul {
		list-style: none;
		float: right;

		li {
			display: inline-block;

			a {
				display: block;
				margin: 10px 20px;
				padding: 5px 3px;
				text-decoration: none;
				color: $default_color;

				&:hover {
					border-bottom: 1px dotted $hover_color;
					color: $hover_color;
				}
			}
		}
	}
}

header {
	background-color: $header_back;
	height: 100px;

	@extend nav;
}

aside {
	width:250px;
	float: left;

	@extend nav;

	ul {
		padding: 0;
		margin-top: 30px;
		float: left;

		li {
			display: block;

			a {
				padding: 5px 10px;
				margin: 0;
				width: 100px;

				&:hover {
					border: 1px solid $aside_hover;
					color: $aside_hover;
				}
			}
		}
	}
}