1834403 - Root element should always establish a stacking context

Status: NEW

(Core :: Layout: Positioned, defect)

Description

[Oriol Brufau [:Oriol]]

Attachment: testcase.html

https://www.w3.org/TR/CSS22/visuren.html#propdef-z-index defines z-index: auto with

If the box has position: fixed or if it is the root, it also establishes a new stacking context.

https://drafts.csswg.org/css-position/#stacking

The root element always forms a stacking context regardless.

Blink and WebKit are correct, the root element always establishes a stacking context.

But Firefox doesn't establish a stacking context for z-index: auto with position: relative or position: absolute.

Comment 1

[Emilio Cobos Álvarez [:emilio]]

I read the normative text as "it's the root box", not the root element's primary box fwiw...

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Should be easy to add an IsRootElememtStyle check to IsStackingContext tho, perhaps.

Comment 3

[Oriol Brufau [:Oriol]]

Isn't the root box always generated by the root element? Since display: contents can't be used on the root element.

Comment 4

[Emilio Cobos Álvarez [:emilio]]

The root box is different from the root element's primary box in Gecko, see this.