Is it possible to set the stacking order of pseudo-elements below their parent element?
Pseudo-elements are treated as descendants of their associated element. To position a pseudo-element below its parent, you have to create a new stacking context to change the default stacking order.
Positioning the pseudo-element (absolute) and assigning a z-index value other than “auto” creates the new stacking context.
#element { position: relative; /* optional */ width: 100px; height: 100px; background-color: blue;}
#element::after { content: ""; width: 150px; height: 150px; background-color: red;
/* create a new stacking context */ position: absolute; z-index: -1; /* to be below the parent element */}
<!DOCTYPE html><html><head> <meta charset="utf-8"> <title>Position a pseudo-element below its parent</title></head><body> <div id="element"> </div></body></html>
How can I put pseudo element behind parent?
To make it work I had to modify your html a bit.
Because of the transformation in .member__profile
a stacking context is created at this level and since the ::before
element is a descendant of his element, z-index
will only move the pseudo element inside .member__profile
.
HTML
<div class="member__profile-container">
<div class="member__profile"></div>
<!-- moved the pseudo-element to a sibling element -->
<!-- removing 'the transform' inside .member__profile and
keeping the pseudo element would also work -->
<div class="member__undercover"></div>
</div>
CSS
.member__profile-container {
/* creating a stacking context on the parent */
position: relative;
z-index: 1;
flex-basis: 50rem;
/* added color to make position clearer */
background-color: green;
}
.member__profile {
position: relative;
padding-top: 150%;
background-image: url('../images/irene.jpg');
/* added color to make position clearer */
background-color: red;
background-repeat: no-repeat;
background-position: center;
background-size: cover;
box-shadow: 0 -1rem .5rem 1rem rgba(0, 0, 0, 0.3);
margin-right: 4rem;
transform: rotate(-5deg) translateX(-10%);
z-index: 0;
}
.member__undercover {
position: absolute;
left: 0;
top: 0;
height: 100%;
width: 100%;
border: 10px solid white;
transform: rotate(-5deg) translateX(-10%);
/* added color to make position clearer */
background-color: blue;
z-index:-1;
}
By using "position: relative; z-index: 1;
" on the container I create a stacking context on this level and can reorder freely it's children with z-index
.
If you use z-index
without creating a stacking context in the container then you will be using a stacking context somewhere else where one has been created in your document, or ultimately the body if none exist before.
If you want the border behind the container not the profile, you just need to move
"position: relative; z-index: 1;
" up one parent (not copy it, move it).
To understand more about the stacking context : MDN, The stacking context
Put Pseudo element behind parent
div {
position: relative; /* optional */
width: 100px;
height: 100px;
background-color: blue;
}
div::after {
content: "";
width: 150px;
height: 150px;
background-color: red;
/* create a new stacking context */
position: absolute;
z-index: -1; /* to be below the parent element */
}
Pseudo-elements are treated as descendants of their associated element. To position a pseudo-element below its parent, you have to create a new stacking context to change the default stacking order.
Positioning the pseudo-element (absolute) and assigning a z-index value other than “auto” creates the new stacking context.
Why can't an element with a z-index value cover its child?
There are two important things you need to know: the painting order and the stacking context. If you refer to the specification, you can find how and when elements are painted.
- Stacking contexts formed by positioned descendants with negative z-indices (excluding 0) in z-index order (most negative first) then tree order.
- All positioned, opacity or transform descendants, in tree order that fall into the following categories:
- All positioned descendants with 'z-index: auto' or 'z-index: 0', in tree order.
- Stacking contexts formed by positioned descendants with z-indices greater than or equal to 1 in z-index order (smallest first) then tree order.
It's clear from this that we first paint elements with negative z-index
at step (3), then the one with z-index
equal to 0 at step (8), and finally the ones with positive z-index
at step (9), which is logical. We can also read in another part of the specification:
Each box belongs to one stacking context. Each box in a given stacking context has an integer stack level, which is its position on the z-axis relative to other boxes in the same stacking context. Boxes with greater stack levels are always formatted in front of boxes with lower stack levels. Boxes may have negative stack levels. Boxes with the same stack level in a stacking context are stacked bottom-to-top according to document tree order.
To understand when each element will be painted you need to know its stacking context and its stack level inside this stacking context (defined by z-index
). You also need to know whether that element establishes a stacking context. This is the tricky part, because setting z-index
will do this:
For a positioned box, the z-index property specifies:
- The stack level of the box in the current stacking context.
- Whether the box establishes a stacking context
Values have the following meanings:
<integer>
This integer is the stack level of the generated box in the current stacking context. The box also establishes a new stacking context.
auto
The stack level of the generated box in the current stacking context is 0. The box does not establish a new stacking context unless it is the root element.
Now we have all the information to better understand each case. If the parent element has a z-index
value of something other than auto
, then it will create a stacking context, thus the child element will be painted inside whatever their z-index
is (negative or positive). The z-index
of the child element will simply tell us the order of painting inside the parent element (this covers your second point).
Now, if only the child element has a positive z-index
and we set nothing on the parent element, then considering the painting order, the child will be painted later (in step (9)) and the parent in step (8). The only logical way to paint the parent above is to increase the z-index
, but doing this will make us fall into the previous case where the parent will establish a stacking context and the child element will belong to it.
There is no way to have the parent above a child element when setting a positive z-index
to the child. Also there is no way to have the parent above the child if we set a z-index
to the parent element different from auto
(either positive or negative).1
The only case where we can have a child below its parent is to set a negative z-index
on the child element and keep the parent at z-index: auto
, thus this one will not create a stacking context and following the painting order the child will be painted first.
In addition to z-index
, there are other properties that create a stacking context. In case you face an expected stacking order, you need to consider those properties, too, in order to see if there is a stacking context created.
Some important facts that we can conclude from the above:
- Stacking contexts can be contained in other stacking contexts, and together create a hierarchy of stacking contexts.
- Each stacking context is completely independent of its siblings: only descendant elements are considered when stacking is processed.
- Each stacking context is self-contained: after the element's contents are stacked, the whole element is considered in the stacking order of the parent stacking context. ref
1: there is some hacky ways if we consider the use of 3D transformation.
Example with an element going under its parent element even if this one has a z-index
specified.
.box {
position:relative;
z-index:0;
height:80px;
background:blue;
transform-style: preserve-3d; /* This is important */
}
.box > div {
margin:0 50px;
height:100px;
background:red;
z-index:-1; /* this will do nothing */
transform:translateZ(-1px); /* this will do the magic */
}
<div class="box">
<div></div>
</div>
z-Index behaviour on pseudo elements
You would have to give pseudo elements a negative z-index to get it to go behind it's parent, plus remove the z-index on the parent.
http://jsfiddle.net/jklm313/Kq2PY/4/
div{
position:relative;
background: #000;
padding: 10px;
}
div:after{
content: '';
position: absolute;
z-index: -1; /* <= not working:( */
background: #3d3;
left: 20px;
top: 20px;
width: 30px;
height: 30px;
}
<div>erferf</div>
z-index for pseudo :after not placed under parent element
Remove the z-index
of the parent
That will give the pseudo elements will have their own stacking context (as you have position: absolute
already applied). Here's an updated fiddle. Hope this helps!
Pseudo elements get hidden when parent uses background
You could translate the parent in the negative z axis. I'm not sure if that's an option for your overall project but in this context, it works.
.parent {
background: yellow;
transform: translateZ(-1px)
}
#element {
position: relative;
/* optional */
width: 100px;
height: 100px;
background-color: blue;
}
#element::after {
content: "";
width: 150px;
height: 150px;
background-color: red;
/* create a new stacking context */
position: absolute;
z-index: -1;
/* to be below the parent element */
}
<div class="parent">
<div id="element"></div>
<div id="yellow"></div>
</div>
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