Spring Sale! Save 15% on WordPress books with code: SPRING22
Web Dev + WordPress + Security

CSS: Odd Bug with Colons and Combined Pseudo Elements

According to specification (and these helpful posts by Chris Coyier), CSS pseudo elements like ::before and ::after should be written with two preceding colons. It can be confusing because while pseudo elements are prefixed by two colons, like ::element, pseudo selectors (aka pseudo classes) are prefixed by only one, like :selector. So that’s the context for an odd little CSS bug..

Odd CSS bug

Update: Thanks to Chris Coyier for pointing out that :last-child actually is a pseudo-selector, not a pseudo-element. Post updated accordingly.

Many browsers continue to support the double-colon prefix for pseudo-elements pseudo-selectors, for example:

li::last-child { margin-right: 0; }

That works fine in most browsers, but does not work when combined with pseudo elements like ::before and ::after. So if you do this:

li::last-child:after { content: ''; }

..it won’t work. And likewise using the double-colon syntax :: for both selectors, for example like this:

li::last-child::after { content: ''; }

Also doesn’t work. For some reason, at least with webkit browsers (e.g., Chrome, Opera, Safari, and many others), in order to combine pseudo elements, you need to use the single-colon syntax for the first element:

li:last-child:after { content: ''; }

..works as expected. Interestingly enough, this works as well:

li:last-child::after { content: ''; }

The take home message: if you’re combining pseudo elements, the first pseudo element must be single-colon prefixed. It doesn’t matter (apparently) on the second pseudo element.

To help visualize slash summarize all of this, I put together a simple demo for combined pseudo elements »

Btw, here is the W3 specification for combining pseudo elements.

Not sure if that is reason enough to stick with single-colon syntax on pseudo elements or not. Maybe it’s a bug? After reading Chris’ article, I wanted to be consistent and use double colons everywhere. But I also need to use combined pseudo elements once in awhile. So do I use both single and double colons? Or stick with single-colon syntax because it always works? Or stick with specification and use only double colons, thereby forfeiting use of any combined pseudo selectors?

Any thoughts or insights welcome :)

Jeff Starr
About the Author
Jeff Starr = Creative thinker. Passionate about free and open Web.
GA Pro: Add Google Analytics to WordPress like a pro.

3 responses to “CSS: Odd Bug with Colons and Combined Pseudo Elements”

  1. While I’m all about best practices, I like to keep things simple, if I can… so I think sticking with :single:single is fine, as long as it continues to function. If it breaks in the future, clients will come running. =)

  2. I thiiiiink the issue here is that like li::last-child is not a pseudo-element, it’s a pseudo selector. So it shouldn’t ever use the double-colon syntax like ::after does. The fact that it ever works with two colons is probably the “bug”, but I can’t super blame browsers for supporting it because I bet there are a ton of sites that mistakenly use it and it would break them to stop.

    • Yes, looks like I was confused about :last-child being a pseudo-element. You’re right it’s a pseudo-selector/pseudo-class. So the “bug” now makes more sense, thanks for your wisdom Chris.

Comments are closed for this post. Something to add? Let me know.
Welcome
Perishable Press is operated by Jeff Starr, a professional web developer and book author with two decades of experience. Here you will find posts about web development, WordPress, security, and more »
USP Pro: Unlimited front-end forms for user-submitted posts and more.
Thoughts
Coding never ends. Bring a snack.
Not posting anything online usually means I’m busy working on my next project.
Today is my 50th B-day :)
Deep in the code.
Making good progress on my next pro plugin, Simple Ajax Chat Pro :)
Events definitely are speeding up. For those who are paying attention.
New wave of spam comments easily blocked, add =https:// to WP Discussion settings ▸ Disallowed Comment Keys.
Newsletter
Get news, updates, deals & tips via email.
Email kept private. Easy unsubscribe anytime.