How to center li when it's floated left - html

Question

Hi this seems to be a common problem, however the solutions I've found haven't worked for me yet :(
I found this however this solution didn't work for me for some reason.
My demo link:
http://leongaban.com/_stack/centering/
I'm trying to get the top nav to center, as well as the Portfolio Nav to center as well.
My JSFiddle:
http://jsfiddle.net/8DM65/
Please help! Driving me nuts X_x
HTML
<header>
<div id="main-nav">
<ul>
<li>Portfolio</li>
<li>Contact Me</li>
<li>Resume</li>
</ul>
</div>
<div id="logo-title">
<img src="images/leon_gaban.png" width="256" height="256" class="avatar" />
<h1>Hello</h1>
<h2>Web Designer & Developer</h2>
<h3>And self-improvement blogger</h3>
</div>
</header>
<section id="content">
<div class="portfolio-nav">
<ul>
<li class="cta">Select Portfolio</li>
<li class="selected">Design & Development</li>
<li class="not-selected">Flash & Animation</li>
</ul>
</div>
<div id="showcase-div">
<ul id="showcase-boxes">
<li>Test</li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
</ul>
</div>
</section>
CSS
/* 02 Header */
header {
width: 100%;
height: 720px;
margin: 0 auto;
background: #ededed;
border-bottom: 1px solid #ccc;
}
header h1 {
font-size: 2em;
font-weight: 400;
font-style: italic;
}
header h2 {
font-size: 3.125em;
font-weight: 700;
}
header h3 {
font-size: 1.125em;
font-weight: 400;
font-style: italic;
}
#logo-title {
width: 100%;
margin: 60px auto;
text-align: center;
}
.avatar {
width: 256px;
height: 256px;
margin-bottom: 20px;
-webkit-border-radius: 128px;
-moz-border-radius: 128px;
-ms-border-radius: 128px;
-o-border-radius: 128px;
border-radius: 128px;
-webkit-box-shadow: 0 0 0px 6px white, 0 0 0 8px #cccccc, 0 10px 40px #333333;
-moz-box-shadow: 0 0 0px 6px white, 0 0 0 8px #cccccc, 0 10px 40px #333333;
box-shadow: 0 0 0px 6px white, 0 0 0 8px #cccccc, 0 10px 40px #333333;
}
#main-nav {
width: 80%;
height: 100px;
margin: 0 auto;
text-align: center;
font-size: 1.5em;
border-bottom: 2px solid white;
}
#main-nav ul {
clear: left;
float: left;
width: 100%;
list-style: none;
padding: 30px 0;
position:relative;
left:50%;
}
#main-nav ul li {
display:block;
position:relative;
right:50%;
float: left;
padding: 0 20px;
}
/* 03 Content */
#content {
width: 100%;
height: 100%;
margin: 0 auto;
}
#content ul {
list-style: none;
}
.portfolio-nav {
height: 60px;
padding: 30px 0 0 0;
background: #ccc;
}
.portfolio-nav ul {
margin: 0 auto;
text-align: center;
}
.portfolio-nav ul li {
display: inline;
float: left;
padding: 0 20px;
text-align: center;
}
#showcase-div {
width: 80%;
height: 100%;
margin: 0 auto;
background: blue;
padding-bottom: 60px;
}

Answer 1

You've actually added too much CSS to these elements and appear to be coding yourself in the wrong direction. I would scrap all the position: relative; stuff and instead focus on building your li's around inline-block. That makes the li's not expand width-wise push each other into a vertical stack.
#main-nav ul li {
display: inline-block;
padding: 0 20px;
}
#main-nav ul {
list-style: none;
padding: 30px 0;
}

Answer 2

Why have you gone with a big mixture of floats, clears, display and positioning? You need to remove a lot of code if you're going to make any sense of what you're doing.
For example, that first navigation. You don't need to display the list-items as block-level elements, and then float them, and then clear them, and then try and position them halfway across the page.
They are list-items, and you want to display them inline.
#main-nav ul {
width: 100%;
list-style: none;
padding: 30px 0;
}
#main-nav ul li {
display: inline;
padding: 0 20px;
}
http://jsfiddle.net/8DM65/2/

Answer 3

It appears I can get this to work very easily with the following:
.portfolio-nav{
text-align: center;
}
.portfolio-nav > ul{
display: inline-block;
}

Answer 4

What i found was that changing the #main-nav width css to 35% fixed it but removes the extra white separator line, so you could add an hr tag with a color of white to fix that. To fix the #portfolio-nav, I changed the width to 44% and added margin: 0 auto.