Responsive Flat Horizontal Menu

<nav class="mega-nav" aria-label="Main">
<button id="resp-menu" class="responsive-menu" type="button" aria-expanded="false" aria-controls="main-menu"><i class="fa fa-reorder" aria-hidden="true"></i> Menu</button>    
   <ul class="menu" id="main-menu">
   <li><a class="homer" href="#"><i class="fa fa-home" aria-hidden="true"></i> HOME</a>
   <ul class="sub-menu">
   <li><a href="#">Sub-Menu 1</a></li>
   <li><a href="#">Sub-Menu 2</a></li>
   <li><a href="#">Sub-Menu 3</a></li>
   <li><a href="#">Sub-Menu 4</a></li>
   <li><a href="#">Sub-Menu 5</a></li>   
   </ul>
   </li>
  <li><a  href="#"><i class="fa fa-user" aria-hidden="true"></i> ABOUT</a></li>
  <li><a  href="#"><i class="fa fa-camera" aria-hidden="true"></i> PORTFOLIO</a>
  <ul class="sub-menu">
   <li><a href="#">Sub-Menu 1</a></li>
   <li><a href="#">Sub-Menu 2</a>
    <ul>
    <li><a href="#">Sub Sub-Menu 1</a></li>
   	<li><a href="#">Sub Sub-Menu 2</a></li>
	<li><a href="#">Sub Sub-Menu 3</a></li>
   	<li><a href="#">Sub Sub-Menu 4</a></li>
	<li><a href="#">Sub Sub-Menu 5</a></li>	
    </ul>
   </li>
     <li><a href="#">Sub-Menu 3</a>
    <ul>
    <li><a href="#">Sub Sub-Menu 1</a></li>
   	<li><a href="#">Sub Sub-Menu 2</a></li>
	<li><a href="#">Sub Sub-Menu 3</a></li>
   	<li><a href="#">Sub Sub-Menu 4</a></li>
	<li><a href="#">Sub Sub-Menu 5</a></li>	
    </ul>
   </li>
   </ul>
  </li>
  <li><a  href="#"><i class="fa fa-bullhorn" aria-hidden="true"></i> BLOG</a></li>
    <li><a  href="#"><i class="fa fa-tags" aria-hidden="true"></i> CATEGORIES</a>
  <ul class="sub-menu">
   <li><a href="#">Sub-Menu 1</a></li>
   <li><a href="#">Sub-Menu 2</a>
    <ul>
    <li><a href="#">Sub Sub-Menu 1</a></li>
   	<li><a href="#">Sub Sub-Menu 2</a></li>
	<li><a href="#">Sub Sub-Menu 3</a></li>
   	<li><a href="#">Sub Sub-Menu 4</a></li>
	<li><a href="#">Sub Sub-Menu 5</a></li>	
    </ul>
   </li>
     <li><a href="#">Sub-Menu 3</a>
    <ul>
    <li><a href="#">Sub Sub-Menu 1</a></li>
   	<li><a href="#">Sub Sub-Menu 2</a></li>
	<li><a href="#">Sub Sub-Menu 3</a></li>
   	<li><a href="#">Sub Sub-Menu 4</a></li>
	<li><a href="#">Sub Sub-Menu 5</a></li>	
    </ul>
   </li>
   </ul>
  </li>
  <li><a  href="#"><i class="fa fa-envelope" aria-hidden="true"></i> CONTACT</a></li>
  <li><a  href="#"><i class="fa fa-sitemap" aria-hidden="true"></i> SITEMAP</a></li>
  <li><a  href="#"><i class="fa fa-exclamation-triangle" aria-hidden="true"></i> DISCLAIMER</a></li>
  </ul>
  </nav>

@import url("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css");

@import url("https://fonts.googleapis.com/css?family=Open+Sans:400,400italic,600,700,800");

body {
    background: #e5e5e5;
    color: #374147;
    font: 14px "Open Sans",Helvetica,Arial,sans-serif;
    line-height: 1;
    margin: 0;
}

.mega-nav, .mega-nav * {
    box-sizing: border-box;
}

.mega-nav ul {
    list-style: none;
    margin: 0;
    padding: 0;
}

.mega-nav a {
    color: #BA0707;
    text-decoration: none;
}

.mega-nav a:hover {
    color: #BA0707;
}

.mega-nav {
    display: block;
    background: #374147;
}

.menu {
    display: block;
}

.menu li {
    display: inline-block;
    position: relative;
    z-index: 100;
}

.menu li:first-child {
    margin-left: 0;
}

.menu li a {
    font-weight: 600;
    text-decoration: none;
    padding: 20px 15px;
    display: block;
    color: #fff;
    transition: all 0.2s ease-in-out 0s;
}

.menu li a:hover,.menu li:hover>a {
    color: #fff;
    background: #9ca3da;
}

.menu ul {
    visibility: hidden;
    opacity: 0;
    margin: 0;
    padding: 0;
    width: 170px;
    position: absolute;
    left: 0px;
    background: #fff;
    z-index: 99;
    transform: translate(0,20px);
    transition: all 0.2s ease-out;
}

.menu ul:after {
    bottom: 100%;
    left: 20%;
    border: solid transparent;
    content: " ";
    height: 0;
    width: 0;
    position: absolute;
    pointer-events: none;
    border-color: rgba(255, 255, 255, 0);
    border-bottom-color: #fff;
    border-width: 6px;
    margin-left: -6px;
}

.menu ul li {
    display: block;
    float: none;
    background: none;
    margin: 0;
    padding: 0;
}

.menu ul li a {
    font-size: 12px;
    font-weight: normal;
    display: block;
    color: #797979;
    background: #fff;
}

.menu ul li a:hover,.menu ul li:hover>a {
    background: #9ca3da;
    color: #fff;
}

.menu li:hover>ul,
.menu li:focus-within>ul {
    visibility: visible;
    opacity: 1;
    transform: translate(0,0);
}

.menu ul ul {
    left: 169px;
    top: 0px;
    visibility: hidden;
    opacity: 0;
    transform: translate(20px,20px);
    transition: all 0.2s ease-out;
}

.menu ul ul:after {
    left: -6px;
    top: 10%;
    border: solid transparent;
    content: " ";
    height: 0;
    width: 0;
    position: absolute;
    pointer-events: none;
    border-color: rgba(255, 255, 255, 0);
    border-right-color: #fff;
    border-width: 6px;
    margin-top: -6px;
}

.menu li>ul ul:hover {
    visibility: visible;
    opacity: 1;
    transform: translate(0,0);
}

.responsive-menu {
    display: none;
    border: 0;
    text-align: left;
    font-family: inherit;
    font-size: inherit;
    width: 100%;
    padding: 20px 15px;
    background: #374147;
    color: #fff;
    text-transform: uppercase;
    font-weight: 600;
}

.responsive-menu:hover {
    background: #374147;
    color: #fff;
    text-decoration: none;
}

.mega-nav a.homer {
    background: #9ca3da;
}

@media (min-width: 768px) and (max-width: 979px) {
    .menu ul {
        top: 37px;
    }

    .menu li a {
        font-size: 12px;
    }

    .mega-nav a.homer {
        background: #374147;
    }
}

@media (max-width: 767px) {
    .menu {
        display: none;
    }

    .menu.open {
        display: block;
    }

    .responsive-menu {
        display: block;
    }

    nav {
        margin: 0;
        background: none;
    }

    .menu li {
        display: block;
        margin: 0;
    }

    .menu li a {
        background: #fff;
        color: #797979;
    }

    .menu li a:hover,.menu li:hover>a {
        background: #9ca3da;
        color: #fff;
    }

    .menu ul {
        visibility: hidden;
        opacity: 0;
        top: 0;
        left: 0;
        width: 100%;
        transform: initial;
    }

    .menu li:hover>ul,
    .menu li:focus-within>ul {
        visibility: visible;
        opacity: 1;
        position: relative;
        transform: initial;
    }

    .menu ul ul {
        left: 0;
        transform: initial;
    }

    .menu li>ul ul:hover {
        transform: initial;
    }
}

function initMobileMenu() {
  var toggle = document.getElementById('resp-menu');
  var menu = document.querySelector('.mega-nav .menu');
  if (!toggle || !menu) return;
  toggle.addEventListener('click', function () {
    var open = menu.classList.toggle('open');
    toggle.setAttribute('aria-expanded', open);
  });
}
initMobileMenu();