Display: Contents Is Not a CSS Reset
CSS resets are a collection of CSS styles that undo the default browser styling of many or most HTML elements.
Recently I have seen cases of developers using
display: contents on lists and headings to remove the margins and padding, and generally to visually do what a CSS reset might do. Essentially, they are using
display: contents as a quick and dirty CSS reset.
This is dangerous for accessibility.
I explain why through the following sections of this post, because if I had to research it to be sure then you damn well have to read it.
- What is display: contents?
- Those Accessibility Implications
- Browser and Spec Bugs
- Update: October 17, 2018
- Update: October 22, 2018
What is display: contents?
It might help to identify what we are talking about. You can skip this part if you are already familiar (it goes on for a bit).
In its simplest form,
display: contents exists to visually remove the element’s box and replace it with its content. Essentially, it treats an element as if the element’s opening and closing tags were removed and the content was left naked on the page.
This can have value when applying it to a
<div>-soup page that you want to use CSS grid or flex to lay out. Perhaps you have inherited a Bootstrap page with its rivers of
<div>s and you want to progressively enhance it to use CSS grid.
Ire Aderinokun provides a high-level overview in her post How display: contents; Works, though browsers do not do quite what she asserts.
Hidde de Vries also explains it in his post More accessible markup with display: contents. His post does not, however, look at it quite the way I have seen
display: contents in play.
The CSS 3 specification provides guidance as well:
The element itself does not generate any boxes, but its children and pseudo-elements still generate boxes and text runs as normal. For the purposes of box generation and layout, the element must be treated as if it had been replaced in the element tree by its contents (including both its source-document children and its pseudo-elements, such as
::afterpseudo-elements, which are generated before/after the element’s children as normal).
Note: As only the box tree is affected, any semantics based on the document tree, such as selector-matching, event handling, and property inheritance, are not affected.
This value behaves as
display: noneon replaced elements and other elements whose rendering is not entirely controlled by CSS; see Appendix B: Effects of display: contents on Unusual Elements for details.
Perhaps more interesting is the collection of special cases:
- any other HTML element
Behaves as normal for
Those Accessibility Implications
Today browsers will take an element with
display: contents and drop it from the accessibility tree. If you read my piece on adding table semantics back into
<table> elements with ARIA (after CSS display properties were applied), well, that won’t work here. Not even a tiny bit.
Demo You Can Try
I have embedded a CodePen below, though it is easier to test the debug version as it dumps all the CodePen wrapper code.
Screen Reader Example
I walked through it with NVDA and Firefox to demonstrate it in action. I am trying to navigate by table (T), list (L), button (B), and heading 2 (2). None of them are recognized. It may be worth noting that each of those elements has an ARIA role applied that matches its native role.
Since I made this video I amended the CodePen to contain two
<button>s, one with an
onkeypress event handler and
tabindex="0" to show that it is dead to keyboard users. I did this because you can still click on the other
<button> and it will fire an
To disabuse you of the notion that this is the fault of screen readers, I can assure you that none of the element’s information (including ARIA) makes it to the screen reader. These screen shots are from Chrome 66.
Browser and Spec Bugs
Ten days before my tests, Hidde de Vries had already filed bugs with browsers based on use of
display: contents in grid layouts:
- Firefox bug 1455357: Setting grid item to display:contents resets its accessible role
- Update, 15 May 2018: Verified fixed in Firefox 62.0a1 (20180515220059).
- Update, 22 October 2018: fixed only for lists, as narrowly defined in the original bug.
- Chromium Issue 835455: Element not exposed to accessibility tree when it is set to display: contents
- Safari bug 39630240 (which I cannot see because my AppleID may not have the needed permissions to see it)
After a Twitter conversation this morning with Ilya Streltsyn, he took the initiative to file an issue against the CSS spec:
- CSSWG #2632: [css-display][css-aam][selectors-4] How elements with `display:contents` get focused?
I don’t believe I am the first to have noticed
display: contents used as a CSS reset, but my tweets this morning seemed to catch some folks off guard and also give me some insight into issues.
This is bad behavior by browsers, but until it is fixed, the only acceptable use for `display: contents` is to remove extra divs that you added for your fallback layout but don't need for your grid layout.
Do not use—yet—on semantic elements: <ul>, <nav>, <button>, <header>, etc twitter.com/aardrian/statu…
Interestingly enough, some other change to a web site *after* it was loaded will make the stuff reappear somehow, at least in Firefox. @jcsteh investigated this just the week before last, and we have a bug in Bugzilla under investigation for this problem. Whole Thread: 👇 twitter.com/aardrian/statu…
tl;dr: for me, _the_ use case for display:contents is increased accessibility, which now works nowhere, because of these bugs.
It… It removes it from the CSS box tree too. It has all sorts of bad side effects if you try to use it like that.
Not only does using `display: contents` as a element-reset hack create a major #a11y probem, it's also poorly supported.
Try `all: initial` instead. It resets an element's styles AND it's much better supported:
If the browsers implemented it as it was intended, it would be very useful, allowing you to have semantic markup wrappers that are independent from your layout.
e.g. a <nav> list followed by a search bar and a language selector, laid out as a single grid or flex container.
Indeed there are plenty of sensible reasons to have elements you might not want visually to create a box.
Yes, currently it is broken. Thank you for the excellent point about `display:contents` elements getting focused! I opened an issue in the CSSWG repo about it: github.com/w3c/csswg-draf…, will file bugs for browsers as soon as the spec clarifies this!
For now, please only use
display: contents if you are going to test with assistive technology and can confirm the results work for users.
Update: October 17, 2018
You cannot assume that it is safe to use
display: contents without weighing the risks. Chrome and Safari still dump semantics. The Firefox fix is only a recent update, so Firefox users who were told by screen reader vendors to grab the ESR (which is based on 52) due to screen reader issues are also still impacted.
Given that very public knowledge, some bad advice might be to say:
bugs are temporary and browsers are updated all the time, so I won’t need to be cautious for long. Well, you have to be cautious until the long tail of these browsers has disappeared for your audience.
This update brought to you by my piss-take (below) on an unfortunate tweet (with its missing image alt text).
♠ “Do not use display: contents as it removes semantics from your HTML.” Working with
display: contentswill ruin native HTML semantics in most browsers.
As an aside, I had that photo taken by Jenny Hiseler at the #a11yTOConf after-party, mocked it up and tweeted it that night, and it appeared unexpectedly in Manuel Matuzovic’s slides the next morning. The shirt was a happy coincidence, the weird expression on my face was not.
Update: October 22, 2018
Because I am generally not working with clients on the bleeding-edge stuff, and because I am not using
display: contents, Scott picked out that Firefox did not, in fact, fix the
display: contents universally.
With TPAC going on this week, I know this came up in conversation as well, so the timing is good.
There are two other related bugs:
- Bug 1494196: Element with ARIA role and display: contents doesn’t get an accessible (September 25, 2018)
- Bug 1500416: Dynamic insertion of display: contents elements doesn’t work (October 19, 2018)
Firefox 64 Nightly also shows this bug. Please avoid
display: contents, especially since we now know that even in the one browser that claimed to fix it, it is still broken.
Update: June 21, 2019
Firefox has fixed the bug display: contents removes attributes from a11y tree (such as button). In a very quick test, all looks to be good.
I don’t understand where I would ever want to use this. I’d modify html instead.