css deformed submenu second option and z-index - css

Question

I'm creating a submenu for my website but it needs some little fixes.
First, I can't make the z-index work, is displayed under the content div, in the live example I removed all z-index, and righ now, I really have no idea how this works :(
Second, in the submenu from second option, the box is more large than the first one. I'm trying to fix it but I don't see where the problem is.
/* Sub-menu */
#main-nav ul {
list-style: none;
margin: 0;
padding: 0;
display: none;
position: absolute;
/* rounded corner */
-webkit-border-radius: 8px;
-moz-border-radius: 8px;
border-radius: 8px;
}
#main-nav ul li {
float: none;
display: block;
/* box shadow */
-webkit-box-shadow: inset 0 1px 0 rgba(255, 255, 255, .3), 0 1px 1px rgba(0, 0, 0, .4);
-moz-box-shadow: inset 0 1px 0 rgba(255, 255, 255, .3), 0 1px 1px rgba(0, 0, 0, .4);
box-shadow: inset 0 1px 0 rgba(255, 255, 255, .3), 0 1px 1px rgba(0, 0, 0, .4);
/* rounded corner */
-webkit-border-radius: 8px;
-moz-border-radius: 8px;
border-radius: 8px;
}
#main-nav ul li:last-child {
box-shadow: none;
}
#main-nav ul a {
color: #fff;
background: #474747;
display: block;
white-space: nowrap;
}
#main-nav ul a:hover {
/* gradient */
background: #6a6a6a url(images/nav-bar-bg.png) repeat-x;
background: -webkit-gradient(linear, left top, left bottom, from(#b9b9b9), to(#6a6a6a));
background: -moz-linear-gradient(top, #b9b9b9, #6a6a6a);
background: linear-gradient(-90deg, #b9b9b9, #6a6a6a);
background-image: linear-gradient(-90deg, #cdcdcd, #797979);
}
#main-nav ul li:first-child a {
/* rounded corner */
-webkit-border-radius: 8px 8px 0 0;
-moz-border-radius: 8px 8px 0 0;
border-radius: 8px 8px 0 0;
}
#main-nav ul li:last-child a {
/* rounded corner */
-webkit-border-radius: 0 0 8px 8px;
-moz-border-radius: 0 0 8px 8px;
border-radius: 0 0 8px 8px;
}
#main-nav ul li:first-child a:after {
content:'';
position: absolute;
left: 30px;
top: -8px;
border-left: 8px solid transparent;
border-right: 8px solid transparent;
border-bottom: 8px solid #444;
}
#menu ul li:first-child a:hover:after {
border-bottom-color: #fafafa;
}
#main-nav:after {
visibility: hidden;
display: block;
font-size: 0;
content:" ";
clear: both;
height: 0;
}
Here's a live example: http://jsfiddle.net/y59kjsLn/1/
Thanks in advance!
Edit: add more css
.clearfix:after {
visibility: hidden;
display: block;
font-size: 0;
content: " ";
clear: both;
height: 0;
}
.clearfix { display: inline-block; }
.clearfix { display: block; zoom: 1; }
Chan this cause the z-index problem?
Edit2: Add the html code
Hmmm maybe has something to do with...
<div id="content">
<article class="post clearfix">
<?php
if(array_key_exists($matches[1], $includes)) {
$content = include($includes[$matches[1]]);
} else header("Location: /home");
?>
</article>
</div>
This is just behind the menu.
#content CSS code:
#content {
opacity: 0.8;
background: #fff;
margin: 30px 0 30px;
padding: 20px 35px;
width: 600px;
float: left;
/* rounded corner */
-webkit-border-radius: 8px;
-moz-border-radius: 8px;
border-radius: 8px;
/* box shadow */
-webkit-box-shadow: 0 1px 3px rgba(0,0,0,.4);
-moz-box-shadow: 0 1px 3px rgba(0,0,0,.4);
box-shadow: 0 1px 3px rgba(0,0,0,.4);
}
#content .error {
color: red;
text-align: center;
}
#content .note {
font-size: 80%;
text-align: center;
}
#content p {
margin-top: 30px;
}
h2.post-title {
margin-top: 15px;
background: #888;
border-radius: 5px;
padding: 0px 5px ;
border-top: 1px solid #889;
border-bottom: 1px solid #889;
text-align: center;
}
h2.post-title a {
color: #FFFFFF;
font-size: 0.9em;
text-shadow: 1px 1px 2px #333333;
}
.post {
margin-bottom: 20px;
}
.post-title {
margin: 0 0 5px;
padding: 0;
font: bold 26px/120% Arial, Helvetica, sans-serif;
}
.post-title a {
text-decoration: none;
color: #000;
}
.post-meta {
margin: 0 0 10px;
font-size: 90%;
}
figure.post-imagen img {
float: left;
margin: 5px;
max-width: 260px;
}
.clearfix:after {
visibility: hidden;
display: block;
font-size: 0;
content: " ";
clear: both;
height: 0;
}
.clearfix { display: inline-block; }
.clearfix { display: block; zoom: 1; }

Answer 1

Js Fiddle
removed the margin which was affecting the sub menu
#main-nav li:first-child {
margin-left: 10px;
}
edit
Remove and Add
#content
opacity: 0.8; /* removed */
background: rgba(255, 255, 255, 0.55); /* added */
}