So if I understand z-index
correctly, it would be perfect in this situation:
The z-index property only works on elements with a position value other than static
(e.g. position: absolute;
, position: relative;
, or position: fixed
).
There is also position: sticky;
that is supported in Firefox, is prefixed in Safari, worked for a time in older versions of Chrome under a custom flag, and is under consideration by Microsoft to add to their Edge browser.
Important
For regular positioning, be sure to include position: relative
on the elements where you also set the z-index
. Otherwise, it won't take effect.
Your elements need to have a position
attribute. (e.g. absolute
, relative
, fixed
) or z-index
won't work.
In many cases an element must be positioned for z-index
to work.
Indeed, applying position: relative
to the elements in the question would likely solve the problem (but there's not enough code provided to know for sure).
Actually, position: fixed
, position: absolute
and position: sticky
will also enable z-index
, but those values also change the layout. With position: relative
the layout isn't disturbed.
Essentially, as long as the element isn't position: static
(the default setting) it is considered positioned and z-index
will work.
Many answers to "Why isn't z-index working?" questions assert that z-index
only works on positioned elements. As of CSS3, this is no longer true.
Elements that are flex items or grid items can use z-index
even when position
is static
.
From the specs:
4.3. Flex Item Z-Ordering
Flex items paint exactly the same as inline blocks, except that order-modified document order is used in place of raw document order, and
z-index
values other thanauto
create a stacking context even ifposition
isstatic
.5.4. Z-axis Ordering: the z-index property
The painting order of grid items is exactly the same as inline blocks, except that order-modified document order is used in place of raw document order, and
z-index
values other thanauto
create a stacking context even ifposition
isstatic
.
Here's a demonstration of z-index
working on non-positioned flex items: https://jsfiddle.net/m0wddwxs/
Make sure that this element you would like to control with z-index does not have a parent with z-index property, because element is in a lower stacking context due to its parent’s z-index level.
Here's an example:
<section class="content">
<div class="modal"></div>
</section>
<div class="side-tab"></div>
// CSS //
.content {
position: relative;
z-index: 1;
}
.modal {
position: fixed;
z-index: 100;
}
.side-tab {
position: fixed;
z-index: 5;
}
In the example above, the modal has a higher z-index than the content, although the content will appear on top of the modal because "content" is the parent with a z-index property.
Here's an article that explains 4 reasons why z-index might not work: https://coder-coder.com/z-index-isnt-working/
If you set position to other value than static
but your element's z-index
still doesn't seem to work, it may be that some parent element has z-index
set.
The stacking contexts have hierarchy, and each stacking context is considered in the stacking order of the parent's stacking context.
So with following html
div { border: 2px solid #000; width: 100px; height: 30px; margin: 10px; position: relative; background-color: #FFF; }
#el3 { background-color: #F0F; width: 100px; height: 60px; top: -50px; }
<div id="el1" style="z-index: 5"></div>
<div id="el2" style="z-index: 3">
<div id="el3" style="z-index: 8"></div>
</div>
no matter how big the z-index
of el3
will be set, it will always be under el1
because it's parent has lower stacking context. You can imagine stacking order as levels where stacking order of el3
is actually 3.8 which is lower than 5.
If you want to check stacking contexts of parent elements, you can use this:
var el = document.getElementById("#yourElement"); // or use $0 in chrome;
do {
var styles = window.getComputedStyle(el);
console.log(styles.zIndex, el);
} while(el.parentElement && (el = el.parentElement));
There is a great article about stacking contexts on MDN