I'm studying about stacking contexts and doing some tests with the properties that create a stacking context.
I did several tests and found that, in addition to z-index
, of course, the following properties also create a stacking context:
transform
other than none
;opacity
other than 1
;perspective
.Are there other properties that apply a stacking context?
One or more of the following scenarios will cause an element to establish its own stacking context1 for its descendants:
The root element always holds a root stacking context. This is why you can start arranging elements without having to position the root element first. Any element that doesn't already participate in a local stacking context (generated by any of the other scenarios below) will participate in the root stacking context instead.
Setting z-index
to anything other than auto
on an element that is positioned (i.e. an element with position
that isn't static
).
Note that this behavior is slated to be changed for elements with position: fixed
such that they will always establish stacking contexts regardless of their z-index
value. Some browsers have begun to adopt this behavior, however the change has not been reflected in either CSS2.1 or the new CSS Positioned Layout Module yet, so it may not be wise to rely on this behavior for now.
This change in behavior is explored in another answer of mine, which in turn links to this article and this set of CSSWG telecon minutes.
Another exception to this is with a flex item and a grid item. Setting z-index
will always cause it to establish a stacking context even if it isn't positioned.
Setting opacity
to anything less than 1
.
Transforming the element:
Setting transform
to anything other than none
.
Setting transform-style
to preserve-3d
.
Setting perspective
to anything other than none
.
Creating a CSS region: setting flow-from
to anything other than none
on an element whose content
is anything other than normal
.
In paged media, each page-margin box establishes its own stacking context.
In filter effects, setting filter
to anything other than none
.
In compositing and blending, setting isolation
to isolate
and setting mix-blend-mode
to a value different from normal
In will change, setting will-change
to a property whose any non-initial value would create a stacking context.
In masking, setting clip-path
/mask
with a value other than none
.
Note that a block formatting context is not the same as a stacking context; in fact, they are two completely independent (although not mutually exclusive) concepts.
1 This does not include pseudo-stacking contexts, an informal term that simply refers to things that behave like independent stacking contexts with respect to positioning, but actually participate in their parent stacking contexts.