I'd like to create CSS3 multi-level drop-down menu and I have found a few examples on the Internet.
I decided to use this one because it has nice animations (that unfortunately fail to work well in real life use case): http://www.alessioatzeni.com/wp-content/tutorials/html-css/CSS3-DropdownMenu/index.html
My questions:
The z-index property specifies the stack order of an element. An element with greater stack order is always in front of an element with a lower stack order.
Try giving the Z-indices in order from lower to higher. Make sure other elements on your page are not having already defined z-index.
If that not works, I would like to have a look at your page/code.
z-index is more complicated than it appears. Your elements may be in different "stacking contexts", which means their z-indexes do not interact directly. Trace the two conflicting elements up the DOM hierarchy until you reach a common ancestor. Start assigning your z-indexes there, and work your way back.
Here's an article on stacking contexts: https://developer.mozilla.org/en-US/docs/CSS/Understanding_z-index/The_stacking_context
In the example below, if #content-wrapper overlapped #nav ul li, you would start setting z-index on #header and #content. Depending on the other CSS and markup, you may need to continue down into #nav and #content-wrapper before it works.
<div id="page">
<div id="header">
<div id="nav"><ul><li>etc</li></ul>
</div>
<div id="content">
<div id="content-wrapper">
Blah
</div>
</div>
</div>
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