“How to create an expandable hamburger menu?”

DEMO: How It Looks

HTML

<header class="header">
  <div class="header__menu menu">
    <div class="menu__icon"> <span></span> </div>
    <nav class="menu__body">
      <ul class="menu__list">
        <li> <a data-goto="#home" href="" class="menu__link">Home</a></li>
        <li> <a data-goto="#section-1" href="" class="menu__link">Section 1</a></li>
        <li> <a data-goto="#section-2" href="" class="menu__link">Section 2</a></li>
        <li> <a data-goto="#section-3" href="" class="menu__link">Section 3</a></li>
      </ul>
    </nav>
  </div>
</header>

CSS

body {
	background-color: black; font-family:sans-serif; 
}
header a {
	color: #111 !important;
	text-decoration: none!important;
	font-weight: 200;
	font-size: 2.2rem;
	line-height: 1.2;
	display: block;
}
.header__menu {
	position: fixed;
	top: 34px;
	right: 30px;
	z-index: 10;
}
.menu__icon {
	z-index: 5;
	display: block;
	position: relative;
	width: 50px;
	height: 22px;
	cursor: pointer;
}
.menu__icon span, .menu__icon::before, .menu__icon::after {
	left: 0;
	position: absolute;
	height: 20%;
	width: 100%;
	transition: all 0.3s ease 0s;
	background-color: white;
}
.menu__icon::before, .menu__icon::after {
	content: '';
}
.menu__icon::before {
	top: 0;
}
.menu__icon::after {
	bottom: 0;
}
.menu__icon span {
	top: 50%;
	transform: scale(1) translate(0, -50%);
}
.menu__icon._active span {
	transform: scale(0) translate(0, -50%);
}
.menu__icon._active::before {
	top: 50%;
	transform: rotate(-45deg) translate(0, -50%);
}
.menu__icon._active::after {
	bottom: 50%;
	transform: rotate(45deg) translate(0, 50%);
}
.menu__body {
	position: fixed;
	top: 0;
	right: -99%;
	width: 34%;
	height: 100%;
	background-color: rgba(255, 255, 255, 0.8);
	padding: 100px 30px 30px 30px;
	transition: right 0.3s ease 0s;
	overflow: auto;
}
.menu__body._active {
	right: 0;
}
.menu__list > li {
	flex-wrap: wrap;
	margin-bottom: 30px;
}
.menu__body ul {
	padding-left: 1rem;
	list-style: none;
}

JavaScript

Link the below external Javascript into the bottom of your HTML.

<script type="text/javascript" src="https://blog.identitydesign.us/js/hamburger.js"></script>

With having the hamburger menu on your navigation, your website could look more sophisticated and clean.