style.css

body {
	font-family: arial;
	display: flex;
}

body > header {
	position: fixed;
	/*width: 300px;*/
	margin-left: -3px;
}

h1 {
	white-space: nowrap;
	padding: 7px;
}

header .nav-link {
	color: black;
	text-decoration: none;
	display: block;
	/*border: 1px solid black;*/
	/*border-collapse: collapse;	*/
	padding: 10px 7px;
	white-space: nowrap;
	border-bottom: 1px solid black;
}

header .nav-link:first-of-type {
	border-top: 1px solid black;
}

header .nav-link:hover {
	background-color: rgb(221, 225, 227);
}

main {
	margin-left: 235px;
	border-left: 1px solid gray;
	padding: 8px;
}

p {
	text-align: justify;
}

code {
	background-color: rgb(230, 235, 240);
	padding: 5px;
	margin-left: 10px;
	display: inline-block;
}

@media only screen and (max-width: 425px) {
	body {
		display: block;
		/*max-width: 100%;*/
    /*overflow-x: hidden;
    	width: 100%;*/
	}

	body > header {
		/*width: 100%;*/
		position: static;
		text-align: center;
		max-width: 100%;
	}

	main {
		margin: 0px;
		border-left: none;
	}

	ul {
		padding-left: 16px;
	}