Wrap the menu contents with another div:
<div id="floatingMenu">
<div>
<a href="http://www.google.com">Test 1</a>
<a href="http://www.google.com">Test 2</a>
<a href="http://www.google.com">Test 3</a>
</div>
</div>
And the CSS:
#floatingMenu {
clear: both;
position: fixed;
width: 100%;
height: 30px;
background-color: #78AB46;
top: 5px;
}
#floatingMenu > div {
margin: auto;
text-align: center;
}
And about your page below the menu, you can give it a padding-top as well:
#content {
padding-top: 35px; /* top 5px plus height 30px */
}