'transform3d' not working with position: fixed children
I have a situation where, in normal CSS circumstances, a fixed div would be positioned exactly where it is specified (top:0px, left:0px).
This does not seem to be respected if I have a parent that has a translate3d transform. Am I not seeing something? I have tried other webkit-transform like style and transform origin options but had no luck.
I have attached a JSFiddle with an example where I would have expected the yellow box be at the top corner of the page rather than inside of the container element.
You can find below a simplified version of the fiddle:
How can I make translate3d work with fixed-positioned children?
Answer
This is because the transform creates a new local coordinate system, as per W3C spec:
In the HTML namespace, any value other than
nonefor the transform results in the creation of both a stacking context and a containing block. The object acts as a containing block for fixed positioned descendants.
This means that fixed positioning becomes fixed to the transformed element, rather than the viewport.
There's not currently a work-around that I'm aware of.
It is also documented on Eric Meyer's article: Un-fixing Fixed Elements with CSS Transforms.