Resonsive Navigation für Mobile, Tablet & Desktop

Halloo, ich brauche eine responsive Navigation für Mobile, Tablet & Desktop Anwendungen.
Momentan habe ich die Navigation an meine Bildschirmgröße mit 180px angepasst,
allerdings weiß ich nicht wie ich nun weiter komme

Mein css file dazu:
nav ul ul {
display: none;
}

nav ul li:hover > ul {
display: block;
}

nav ul {
background: #efefef;
background: linear-gradient(top, #efefef 0%, #56b29e 90%);
background: -moz-linear-gradient(top, #efefef 0%, #56b29e 90%);
background: -webkit-linear-gradient(top, #efefef 0%, #56b29e 90%);
box-shadow: 0px 0px 9px rgba(86, 178, 158, 0.15);
padding: 0 20px;
border-radius: 10px;
list-style: none;
position: relative;
display: inline-table;
}
nav ul:after {
content: ""; clear: both; display: block;
}

nav ul li {
float: left;
}
nav ul li:hover {
background: #4b545f;
background: linear-gradient(top, #4f5964 0%, #5f6975 40%);
background: -moz-linear-gradient(top, #4f5964 0%, #5f6975 40%);
background: -webkit-linear-gradient(top, #4f5964 0%,#5f6975 40%);
}
nav ul li:hover a {
color: #fff;
}

nav ul li a {
display: block; padding: 16px 180px;
color: rgba(0, 0, 0, 0.98); text-decoration: none; font-size:13pt;
}

nav ul ul {
background: #5f6975; border-radius: 0px; padding: 0;
position: absolute; top: 100%;
}
nav ul ul li {
float: none;
border-top: 1px solid #6b727c;
border-bottom: 1px solid #575f6a;
position: relative;
}
nav ul ul li a {
padding: 15px 40px;
color: #fff;
}
nav ul ul li a:hover {
background: #4b545f;
}

Mein html file:

<nav>
<ul>
<li><a href="DesignVorlage.html">Übersicht</a>
<ul>
<li><a href="#">Übersicht 1</a></li>
<li><a href="#">Übersicht 2</a></li>
</ul>
</li>
<li><a href="Taetigkeitenerfassung.php">Tätigkeit</a></li>
<li><a href="index.php"><span class="glyphicon glyphicon-log-out"></span> Abmelden</a></li>
</ul>
</nav>