Chrome and Safari ignoring (?) position:absolute - html

Question

Have a look at http://www.habitatlandscape.co.uk/
In Firefox and even Internet Explorer (!!!) the pop-up menus appear perfectly, vertically centered in the white strip, and always starting on the far-left-hand-side.
In Chrome, the menus start horizontally under the parent li, and are not centered vertically. I can fix the vertical alignment by targetting webkit with a different position, but I can't fix the horizontal alignment.
Why is Webkit ignoring position:absolute;left:0;?
CSS:
#header #menu
{
margin:0;
padding:0;
}
#header #menu ul
{
list-style-type:none;
margin:0;
padding:0;
margin-top:28px;
height:24px;
}
#header #menu ul li
{
display:inline;
position:relative;
}
#header #menu ul li a
{
display:block;
float:left;
padding:7px;
padding-bottom:3px;
background:#fff;
margin-right:5px;
text-decoration:none;
-webkit-border-top-left-radius: 5px;
-webkit-border-top-right-radius: 5px;
-moz-border-radius-topleft: 5px;
-moz-border-radius-topright: 5px;
border-top-left-radius: 5px;
border-top-right-radius: 5px;
font-family:'museo', serif;
font-size:12px;
text-transform:uppercase;
color:#fff;
font-weight:bold;
padding-left:12px;
padding-right:12px;
background:#01973D;
position:relative;
z-index:2;
}
#header #menu ul li:hover a
{
background:#00BB4A;
}
#header #menu ul li ul
{
clear:both;
display:none;
position:absolute;
top:39px;
width:700px;
margin:0;
padding:0;
}
#header #menu ul li ul li
{
display:block;
}
#header #menu ul li ul li a
{
background:#fff !important;
color:#000;
font-weight:normal;
padding:7px;
padding-left:11px;
color:#01973D;
padding-top:10px;
margin:0;
float:left;
}
#header #menu ul li ul li a:hover
{
color:#000;
}
#header #menu ul li:hover ul
{
display:block;
}
HTML (CMS-generated):
<div id="menu">
<ul>
<li class="parent"><a class="parent" href="http://www.habitatlandscape.co.uk/about-us/"><span>About Us</span></a>
<ul>
<li><span>Company History</span></li>
<li><span>Meet The Team</span></li>
</ul>
</li>
<li class="parent"><a class="menuactive parent" href="http://www.habitatlandscape.co.uk/portfolio/"><span>Portfolio</span></a>
<ul>
<li><span>View before, during and after photos from recent projects</span></li>
</ul>
</li>
<li class="parent"><a class="parent" href="http://www.habitatlandscape.co.uk/services/"><span>Services</span></a>
<ul>
<li><span>Design</span></li>
<li><span>Patios</span></li>
<li><span>Decking</span></li>
<li><span>Turf</span></li>
<li><span>Ponds</span></li>
<li><span>Driveways</span></li>
<li><span>Fencing</span></li>
<li><span>Electrics</span></li>
<li><span>Structures</span></li>
</ul>
</li>
</ul>
// etc
</div>

Answer 1

You've created a mess by display:inline-ing your <li> elements but display:block-ing your <a> elements.
In HTML, it's invalid to nest a block-level element in an inline element:
<span><div>FAIL</div></span>
When you do something like this, you're going to have cross-browser problems. The same goes if you use CSS to change the display property:
<div style="diplay:inline"><span style="display:block">STILL A FAIL</span></div>
Which is what you've done:
#header #menu ul li {
display: inline;
/* ... */
}
#header #menu ul li a {
display:block;
/* ... */
}
That behavior is more or less undefined as far as the specs are concerned (since it makes no sense) so the browser reserves the right to do something insane or ridiculous - which is what you're seeing. It works in Firefox only because you're getting lucky and it works in Internet Explorer because Internet Explorer is inherently insane and ridiculous.
If you want those <li> elements to stack horizontally, float:left them instead of inlining them. Then you can display:block your <a> element without issue. Once that's done you'll still have to switch up which elements are position:relative;-ed, and probably add a left:0 somewhere.
Here's an example of your current issue on jsfiddle, and here's an example of my suggested fix on jsfiddle, which involves positioning the #header #menu ul element relatively instead of the #header #menu ul li.

Answer 2

When I gave the #header #menu ul li a display:inline-block; it fixed it. It also changed the result of the hidden ul's top positioning, which should be 24px to match the height if the button anyways, right?