How to ignore parent element's overflow:hidden in css

Method 1

A good way to do it is by setting the overflowing element to position:fixed (which will make it ignore the parent overflow), and then positioning it relative to the parent using this technique:

​.parent {
   position: relative;      
   .fixed-wrapper {
       position: absolute;         
       .fixed {
           position: fixed;
       }
   }
}

One caveat is that you cannot have any of the top,right,left,bottom properties set on the fixed element (they must all be default 'auto'). If you need to adjust the position slightly, you can do so using positive/negative margins instead.

Method 2

Another trick I recently discovered is to keep the overflow:hidden element with position:static and position the overriding element relative to a higher parent (rather than the overflow:hidden parent). Like so:

http://jsfiddle.net/kv0bLpw8/

CSS

<style type="text/css">
#wrapper {
    width: 400px;
    height: 50px;
    position: relative;
    z-index: 1000;
    left: 0px;
    top: 0px;
}

#wrapper #insideDiv {
    width: 400px;
    height: 50px;
    overflow: hidden;
    position: absolute;
    z-index: 2000;
    left: 0px;
    top: 0px;
}

#wrapper #a {
    position: absolute;
    height: 30px;
    width: 100px;
    bottom: -40px;
    z-index: 1000;
    left: 0px;
}
</style>

HTML

<div id="wrapper">
  <div id="a">AAA</div>
  <div id="insideDiv">
    <div id="b">BBB</div>
  </div>
</div>