<div class="main">
  <nav>
    <ul class="menu">
      <li><a>HOME</a></li>
      <li><a>ABOUT</a></li>
      <li><a>WORK</a></li>
      <li><a>CONTACT</a></li>
    </ul>
  </nav>
  <p>SCROLL DOWN!</p>
</div>
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: "Lato";
  color: #4a4a4a;
}

.main {
  width: 40em;
  height: 300vh;
  margin: 0 auto;
  background: silver;
}

.main p {
  font-size: 30px;
  text-align: center;
  padding-top: 150px;
}

.menu {
  position: fixed;
  text-align: center;
}

.menu li {
  background-color: #32557f;
  color: #fff;
  list-style-type: none;
  display: inline-block;
  padding: 15px 0;
  margin-right: -4px;

  border-top: 1px solid #fff;
  border-bottom: 1px solid #fff;
  border-left: 1px solid #fff;
}

.menu li:last-child {
  border-right: 1px solid #fff;
}

.menu a {
  display: block;
  width: 10em;
}

.menu-scroll li {
  padding: 5px 0;
}

nav,
a,
li {
  transition: 0.7s all;
}
$(window).scroll(function() {
    if ($(document).scrollTop() > 200) { 
        $('.menu').addClass('menu-scroll'); 
    } else {
        $('.menu').removeClass('menu-scroll');
    }
});

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js