Create Toggle Button in HTML CSS and JavaScript

I have the following code to show a vertical sidebar on my page. This vertical sidebar shows the menu items on my page

<div id="mySidebar" class="sidebar">
    <a href="javascript:void(0)" class="closebtn" onclick="closeNav()">×</a>
    <a href="#">About</a>
    <a href="#">Services</a>
    <a href="#">Clients</a>
    <a href="#">Contact</a>
</div>

This is the stylessheet:

<button class="openbtn" onclick="openNav()">☰ Open Sidebar</button>

These are the menu items:

<style>
body {
  font-family: "Lato", sans-serif;
}

.sidebar {
  height: 100%;
  width: 0;
  position: fixed;
  z-index: 1;
  top: 0;
  left: 0;
  background-color: red;
  overflow-x: hidden;
  transition: 0.5s;
  padding-top: 60px;
}

.sidebar a {
  padding: 8px 8px 8px 32px;
  text-decoration: none;
  font-size: 25px;
  color: #818181;
  display: block;
  transition: 0.3s;
}

.sidebar a:hover {
  color: #f1f1f1;
}

.sidebar .closebtn {
  position: absolute;
  top: 0;
  right: 25px;
  font-size: 36px;
  margin-left: 50px;
}

.openbtn {
  font-size: 20px;
  cursor: pointer;
  background-color: #111;
  color: white;
  padding: 10px 15px;
  border: none;
}

.openbtn:hover {
  background-color: #444;
}

#main {
  transition: margin-left .5s;
  padding: 16px;
}

/* On smaller screens, where height is less than 450px, change the style of the sidenav (less padding and a smaller font size) */
@@media screen and (max-height: 450px) {
  .sidebar {padding-top: 15px;}
  .sidebar a {font-size: 18px;}
}
</style>

This is the Javascript:

<script>
    function openNav() {
        document.getElementById("mySidebar").style.width = "250px";
        document.getElementById("main").style.marginLeft = "250px";
    }

    function closeNav() {
        document.getElementById("mySidebar").style.width = "0";
        document.getElementById("main").style.marginLeft = "0";
    }
</script>

I dont want to use "X" to close the sidebar. I want to use this button "☰ Open Sidebar" to behave like a toggle button to close and open the sidebar if I click on it, sidebar opens and if I click on it again then sidebar closes. Right now, the sidebar opens with "☰ Open Sidebar" this button and closes with "X" button. 

any help will be appreciated.