<div class="header">
  <div class="navbar"></div>
  <div class="menu"></div>
</div>

.menu {
  background: #000;
  width: 200px;
  height: 400px;
  position:sticky;
  position: -webkit-sticky;
    border:4px solid green;
  top: 0;
}
.navbar {
  background: gray;
  height: 100px;
  margin-bottom: 20px;
}
.header {
   height: 500vh;
}