html

    <nav class="active" id="nav">
      <ul>
        <li><a href="#">Home</a></li>
        <li><a href="#">Works</a></li>
        <li><a href="#">About</a></li>
        <li><a href="#">Contact</a></li>
      </ul>
      <button class="icon" id="toggle">
        <div class="line line1"></div>
        <div class="line line2"></div>
      </button>
    </nav>

css

@import url('https://fonts.googleapis.com/css?family=Muli&display=swap');

* {
  box-sizing: border-box;
}

body {
  background-color: #eafbff;
  background-image: linear-gradient(
    to bottom,
    #eafbff 0%,
    #eafbff 50%,
    #5290f9 50%,
    #5290f9 100%
  );
  font-family: 'Muli', sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
}

nav {
  background-color: #fff;
  padding: 20px;
  width: 80px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 3px;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
  transition: width 0.6s linear;
  overflow-x: hidden;
}

nav.active {
  width: 350px;
}

nav ul {
  display: flex;
  list-style-type: none;
  padding: 0;
  margin: 0;
  width: 0;
  transition: width 0.6s linear;
}

nav.active ul {
  width: 100%;
}

nav ul li {
  transform: rotateY(0deg);
  opacity: 0;
  transition: transform 0.6s linear, opacity 0.6s linear;
}

nav.active ul li {
  opacity: 1;
  transform: rotateY(360deg);
}

nav ul a {
  position: relative;
  color: #000;
  text-decoration: none;
  margin: 0 10px;
}