HTML5 Rocks

HTML5 Rocks

Get on the CSS Grid!

By Alex Danilo at

When building a Web Application, one of the first things that’s needed is a way to lay out the content of your app.

Lots of designers use imaginary grids to lay out content, whether it’s for a site or app. The CSS group has been working hard to make layouts easier, and as part of that have produced the CSS Grid Layout Module which is now emerging in browsers.

This feature is available to try out in Chrome behind an experimental flag. It’s also implemented in IE since version 10, and likely to be in most browsers soon.

Executive summary

  • CSS Grid Layout lets you define rows and columns for your layout
  • Grids can adapt to make use of available space
  • Content order can be independent from grid container display order
  • Layouts can change based on media queries, making responsive design easier
  • Content can overlap (enabling layout that’s impossible with other methods)
  • Grid Layout is fast

Here’s an overview video that explains a lot about how CSS Grid Layout works (slides are here):

Try it out

Using CSS Grid Layout in Chrome now is easy. First thing you need to do is turn on the experimental flag to enable the feature.

First load the chrome://flags URL and scroll down to the option to Enable experimental Web Platform features as shown below:

Image of experimental flag option

Just click Enable to turn the flag on, and you should see a prompt to restart the browser that looks like this:

Image of Relaunch button

Now just click the Relaunch Now button to restart your browser and you’ll be all set to try out CSS Grid Layout.

Let us know what you think

CSS Grid Layout is a great new primitive for web content, but as usual we’re all keen to hear what developers think about it. There are lots of ways to give feedback – leave a comment here, send mail to the W3C CSS Working Group list with “[css-grid]” in the subject line, log bugs, or blog and tweet what you think of it. We look forward to seeing the great layouts you build with this super useful new feature.

Flexbox layout isn't slow

By Paul Irish at

TL;DR: Old flexbox (display: box) is 2.3x slower than new flexbox (display: flex).

A bit ago, Wilson Page wrote a great article for Smashing Magazine digging into how they brought the Financial Times webapp to life. In the article, Wilson notes:

As the app began to grow, we found performance was getting worse and worse.

We spent a good few hours in Chrome Developers Tools’ timeline and found the culprit: Shock, horror! — it was our new best friend, flexbox. The timeline showed that some layouts were taking close to 100 milliseconds; reworking our layouts without flexbox reduced this to 10 milliseconds!

Wilson's comments were about the original (legacy) flexbox that used display: box;. Unfortunately they never got a chance to answer if the newer flexbox (display: flex;) was faster, but over on CSS Tricks, Chris Coyier opened that question.

We asked Ojan Vafai, who wrote much of the implementation in WebKit & Blink, about the newer flexbox model and implementation.

The new flexbox code has a lot fewer multi-pass layout codepaths. You can still hit multi-pass codepaths pretty easily though (e.g. flex-align: stretch is often 2-pass). In general, it should be much faster in the common case, but you can construct a case where it's equally as slow.

That said, if you can get away with it, regular block layout (non-float), will usually be as fast or faster than new flexbox since it's always single-pass. But new flexbox should be faster than using tables or writing custom JS-base layout code.

To see the difference in numbers, I made a head-to-head comparison of old v new syntax.

Old v New Flexbox Benchmark

  • old flexbox vs new flexbox (with fallback)
  • 500 elements per page
  • evaluating page load cost to lay out the elements
  • averaged across 3 runs each
  • measured on desktop. (mobile will be ~10x slower)

Old flexbox: layout costs of ~43.5ms

New flexbox: layout costs of ~18.2ms

Summary: Old is 2.3x slower than new.

What should you do?

When using flexbox, always author for the new stuff: the IE10 tweener syntax and the new updated flexbox that’s in Chrome 21+, Safari 7+, Firefox 22+, Opera (& Opera Mobile) 12.1+, IE 11+, and Blackberry 10+. In many cases you can do a fallback to the legacy flexbox to pick up some older mobile browsers.


  • I also ran the benchmark using display:table-cell and it hit 30ms, right between the two flexbox implementations.
  • The benchmarks above only represent the Blink & WebKit side of things. Due to the time of implementation, flexbox is nearly identical across Safari, Chrome & Android.

Remember: Tools, not rules

What’s more important is optimizing what matters. Always use the timeline to identify your bottlenecks before spending time optimizing one sort of operation.

In fact, we've connected with Wilson and the Financial Times Labs team and, as a result, improved the Chrome DevTools coverage of layout performance tooling. We'll soon be adding the ability to view the relayout boundary of an element, and Layout events in the timeline are loaded with details of the scope, root, and cost of each layout: