A Touch of Class


Evolution of CSS Layout: 1990s to the Future

русский язык: Эволюция CSS-вёрстки: с 90-х в будущее

Earlier this year, I was asked to speak at the Emerging Technologies for the Enterprise conference in Philadelphia. I didn't think I'd have anything useful to say at such a conference, not being a practicing web developer, but they scoped out a presentation that seemed like a really interesting idea that I knew I could execute really well. So I agreed to give the talk. Besides, I like Philadelphia. :)

Some topics (like How to File a Good Bug Report) I can throw together a few slides and just wing it. This wasn't going to be one of those. I spent a lot of time preparing over the weeks preceding—most of which was spent writing things out on paper, because I'm kindof analog like that:

After the conference, PhillyETE posted a screencast of the presentation, so anyone can watch it online. If you're at all interested in the evolution of CSS, (and you like videos or prefer listening to reading) you should watch it! I promise it's a good presentation. :)

The Evolution of CSS Layout Screencast with Audio

But if watching videos is not your thing, I've posted my notes below. It's just an HTMLized version of my actual notes (which are mostly just a typeset version of a week of scribbles on paper). I wrote out most of the presentation out in complete sentences before presenting it, so while it's not a true transcript, it'll read like one. (The W3C process stuff is added; I hadn't written out that section because I can practically give a talk about it in my sleep.)

Altogether it was a fun challenge, and I think what came out was worth creating. Thanks to the organizers at Chariot Solutions for scoping out a great presentation!

    Table of Contents

  1. Introduction
  2. The Dark Ages
  3. CSS Level 1
  4. CSS Level 2
  5. CSS2.1 Era
  6. CSS Level 3
  7. About Layout
  8. Web v.s. Print
  9. Principles of Design
  10. CSS3 Layout Modules
  11. Multi-column Layout
  12. Flexible Box Layout
  13. Grid Template Layout
  14. Media Queries
  15. Regions and Exclusions
  16. How CSS Specs Grow Up
  17. Review and Revision
  18. Get Involved!
  19. Addendum

The Evolution of CSS Layout

Through CSS3 and Beyond

Presented by fantasai

Hi! I'm fantasai.
I work on the CSS specifications at W3C.

This is my first time giving a presentation at a conference like this.

  • How many people here work with CSS?
  • How many know what it is, but don't use it?
  • Anyone not know what CSS is?
  • Raise your hand if you have heard of W3C.
  • Keep your hand up if you know what we do. :)
  • Raise your hand if you have no idea what W3C does.

So my day job is working on the CSS specifications. What this means is that I work with guys from Apple, Microsoft, Mozilla, Opera, Adobe, HP, Google, and other companies to design and describe new features for CSS, and, less glamorously, to fix errors and ambiguities in the specifications for existing CSS features.

The specs we write at W3C are what define a correct CSS implementation: they represent an agreement among the browser vendors as to what, exactly, CSS is and how it behaves.

The Dark Ages

First, to understand CSS layout and the mess it is today, we're going to go back in time...

All the way to the late 1990s, the Age of Geocities.

Ok, well, not all web pages looked that horrible. :)

But this was the dark ages of Web Design, when H1 meant "bigger font", when adding background color required table tags, and when the most sophisticated layout tool designers had was HTML tables. With transparent spacer GIFs inside.

CSS Level 1

CSS was created to replace all the formatting markup — all the FONT tags and BR tags — with a simple style sheet language. Using CSS, you could control the style of an entire website with a few lines of code in a single file, and that, at the time, was totally radical.

Now CSS Level 1 didn't have any real layout tools. It had width and height properties, which replaced their namesake HTML attributes; and it had floats, which replaced the align attribute on IMG and TABLE. This was not intended—nor, at that time, used—for coarse layout but for, well, floats. Y'know, with text wrapping around them. Tables were still the accepted way of handling 2D layout; there was nothing else. And of course CSS margins and padding provided a much-needed relief from spacer gifs and BR tags. These things seem very simple to us now, but back then they were revolutionary. :)

CSS Level 2

With CSS Level 2, which was released in 1998, W3C brought the Web's state-of-the-art layout tool to CSS: you could turn any collection of HTML elements into a table display. Together with other values of the 'display' property, CSS2 promised the ability to dissociate the layout you desired from the tags you used, freeing up authors to use more appropriate semantic markup. Navigation lists could be displayed as tab navigation, and equal-height columns became a one-liner in CSS:

Unfortunately, even though there was cross-browser support in Gecko, Opera, and KHTML/Webkit, the lack of support in IE until version 8 made CSS tables unusable on the Web.

And so Web authors, taking heed of advice to use table markup only semantically, began to hack out layouts with complicated mixtures of absolute positioning and floats.

CSS Layout today is mostly built out of this. It's an ingeneous use of the materials available, but a bit like building a house out of duct tape and broomsticks. It's therefore tricky, and difficult to understand or make sense of.

Let's look at what the CSS Working Group was up to in the meantime.

Back in the Ivory Tower...

CSS Timeline
Browser Wars I: Netscape vs. Microsoft
mid 1990s HTML for formatting
late 1990s CSS1 catches on
IE6 Monopoly
early 2000s Web Standards Campaign FTW
Browser Wars II: Phoenix Rising
mid 2000s Quest for Interoperability
Balance of Powers
late 2000s Have interop, will build features.
Browser Wars III: Mobile Edition
early 2010s HTML5 + CSS3 take off

Meanwhile, the CSS Working Group had started on CSS3, and several core modules, like Selectors and Color, were mostly completed. However, we soon realized that what was needed more was interoperability among the browsers. CSS2.0 was riddled with errors and ambiguities, and included several features nobody implemented. The browsers were similarly riddled with standards-compliance bugs and inconsistent behavior, making Web design a nightmare of working around various browsers' quirks.

So in 2002 the CSSWG started CSS 2 Revision 1, beginning a long process of plugging the holes, fixing errors, and building test suites for the core CSS standard. Meanwhile, evangelism efforts like the Acid 2 test helped focus browser dev teams on improving their core CSS support.

It wasn't a very exciting time in CSS development, but it laid the groundwork for a reliable CSS3 standard. As the CSS2.1 effort started to wind down in the late 2000s, CSS3 spec and implementation work started revving back up. CSS2.1 was finally completed in May of last year; and the CSSWG has finally been able to focus all its efforts on CSS3.

CSS Level 3

Beyond level 2 CSS is modularized: what this means is it's split up into parts, that can each progress individually, levelling up at its own pace. CSS3 can be broken down into four major efforts:

  • Processing power: things like Selectors and Media Queries.
  • Decorative effects: things like multiple backgrounds, rounded corners, border images, and CSS gradients
  • Typography and Internationalization: things like vertical text, custom fonts, and line-breaking and justification controls
  • And, probably the most difficult: Layout

(This whole list kindof goes in order from easiest to define and implement down to the most difficult.)

About Layout

It's hard to understand the work that goes into designing and building a layout system if you don't actually work on one—the expected results are so obvious, it seems simple; but the calculations that go into it involve a lot of details. Chapter 10 of CSS2.1, which deals only with calculating widths and heights of elements (and doesn't even touch margin collapsing or floats and clearance or even tables) runs 18 pages long and is the output of many, many hours of excruciatingly detailed technical discussion over more than a decade. And people still find errors in it, nevermind in the browser engines that supposedly implement it.

So layout is hard. And layout for the Web is harder. Let's talk about why. First, we'll talk about layout in Print, and then why it's different from layout for the Web.

Web vs. Print

In Print Media,

  • You know the size of the page.
  • You know the amount of content you have, and in some cases, you can even tweak the content to fit the layout
  • You know the fonts you have, and you control their size.
  • When you ask the computer to lay something out for you, and it get it not quite right, you can tweak it afterwards.
  • And when you're done, exactly what you see is exactly what everyone in your audience gets.

In print, the designer is in control. Not so on the Web. On the Web,

  • Different viewers have different fonts available.
  • Different devices have differently-sized screens,
  • Different resolutions,
  • Different aspect ratios.
  • People resize their windows.
  • They zoom the text size.
  • And they generate content that you don't control, but you have to style.

If content doesn't fit, you can't just clip it. You can't copy-edit it. You can't change the size of the paper, or the size of the font.

You could send a PDF, but nobody wants that because Web content by and large adapts to its environment, and people want that. They want it to fit their screen, use the font-size they're comfortable reading, display the content they wrote.

So we come to some key differences between Web and Print: Web layout has to be

  • flexible
  • adaptable
  • automatic
  • and robust

It can't fail because it's loaded in an environment that wasn't quite what the designer had in mind... because that happens all the time. Especially on my screen, because I have a small laptop and I tend to put two windows side-by-side. :)

CSS3 Layout: Principles of Design

Ok, let's talk about CSS3 Layout. CSS3 is really the first time the CSSWG has attempted to design a system expressly for 2D layout.

And we want to do it right for the Web, which means we want a system that is...


That adapts gracefully to different screen sizes, font sizes, amounts of contents, etc.


That can express most layouts designers want to have and the constraints they want it to flex under. One that makes the simple things easy, and the complex ones possible.


That doesn't break down and become unreadable in unexpected conditions like an unexpected font size, or an unusually long paragraph, or an uncommonly-narrow screen.


Doing layout in CSS right now is complicated, hard to understand, and hard to learn. This is largely because no feature in CSS was intended to do 2D layout. As we intentionally design real layout systems to CSS, we want to make sure the syntax is clear and self-evident, and that the concepts and algorithms make sense and reflect the behaviors authors are most likely to want.


Lastly, the Web is a platform for interactive applications, so a layout system for the Web needs to be performant.

This last part is a bit tricky because there are some layouts people want that can only be solved with an iterative constraint solver. But we want to minimize the cases where that's necessary and make the common cases easier to optimize.

CSS has all of these characteristics for the layout system it has, but that layout system is just one-dimensional layout: single-column flow for long documents. Like CSS specs. What we want is layout tools for two dimensions. And that's what we're building in CSS3.

CSS3 Layout: New Modules

So now I'm going to talk about some upcoming CSS3 modules that are in varying stages of development.

First up is CSS Multi-column Layout.

CSS Multi-column Layout

In some ways, this is the simplest of the CSS layout modules, which is why its spec was completed first, even though it's one of the hardest to implement and probably does the least to solve 2D layout on the Web. But it does show off some of the qualities we just talked about: flexibility and power, robustness and understandability.

Multi-column layout is very simple to use. If you want divide an element into multiple columns of flow, you just give it a column width like this:

article { columns: 30em; }

and then CSS calculates how many columns would fit and splits the flow into that many columns.

If there isn't room for more than one column, then there will be only one column. And if there's room for 5, there will be five columns. You can also specify the max number of columns like this:

article { columns: 30em 4; }

This says give me up to four columns if there's room, but no more than four; and make sure each column is at least 30em wide.

The width you specify isn't an absolute, it's a goal. If 2½ columns will fit, you'll get two columns 45em wide each. If only half a column will fit, you'll get one column 15em wide. So the width might not always be what was specified, but for the reader, the design always fits the screen perfectly. And since the column heights are auto-balanced, the layout always fits the content.

The main problem with CSS Multi-column layout is that on scrolled media, if you have a lot of content, the columns get really long and the reader has to scroll back and forth a lot, which is awkward. It's something we'll need to fix in the next level. But for short content or in paged media, it works great. And it's implemented across browsers right now, so it's something you can use today.

CSS Flexible Box Layout

The next layout module I want to talk about is CSS Flexbox Layout. This module is still being worked out, but it's stabilizing, and we have several experimental implementations. I'd expect it to be released later this year.

Flexbox introduces the concept of flexible sizes, so you can specify sizes as a proportion of the available space. This is pretty useful for things like toolbars.

You can use flexes absolutely, where the proportions you give are the proportions you get; or you can use them relatively, where leftover space is distributed after you've assigned sizes based on the content.

Flexbox layout was originally designed to handle Mozilla's UI, which is implemented in XML+CSS+JS, so the types of layout done in browser UI will be easily available for web apps Very Soon Now.

Grid Template Layout

The third module I wanted to talk about is CSS Grid Layout. This is a module created by putting together Bert Bos's Template Layout proposal with a Grid Layout proposal from Microsoft. We're still in the process of fitting it all together, so the module is not finalized at all; but it will make 2D layout grids a simple and obvious thing to develop with in CSS.

The way it works is that you declare an element to be a grid, give it some row and column sizes, and maybe also a slot template: Then you can assign descendant elements into slots in the grid, either by using the slot names or by positioning it with row/column indices.

I'll note we're still working out the exact syntax for this, so don't go copy-pasting these examples. :) But you might start to see experimental implementations of Grid Layout in the not-too-distant future.

The next modules I wanted to touch on are CSS Regions and Exclusions. These are two proposals from Adobe for doing magazine-style layouts. I want to show these because they're an example of capabilities that came from print and work great in InDesign, but in their current state aren't suitable for the Web.

Regions allows chaining boxes into a common flow, similar to how the different columns in a multi-column element are chained into different flows.

And Exclusions allows for non-rectangular containers and floats.

To take a concrete example, Exclusions and Shapes lets you fill a circle with text. But if you increase the font size a few notches, the text no longer fits and starts to disapear. Currently the proposals handle problems like this by relegating the responsibility for solving them to JavaScript. Which arguably works, but isn't what we're committed to.

To take another concrete example, if you want to put a circular float in the middle of an element sized to fit its content, the position of the float depends on how the float impacts the content, which can be very expensive, performance-wise, to figure out. You can get a fast answer or you can get an accurate one, not both.

The CSSWG is struggling with how to take these proposals—which work fine for fixed-size, known-font, stable-content situations—and make them work in a flexible manner, to make them really work for the diverse input/output environment that is the Web.

Media Queries

Lastly, I wanted to talk about Media Queries, which is a module that is already well-implemented across browsers. Media Queries allow you to tailor and reconfigure your CSS to different output environments.

Here's a design Divya Manian, Jason Cranford Teague, and I put together for the CSS Working Group home page:

CSSWG Proposed Redesign [resize the window]

Watch how the design folds down from 3-columns to 2-columns to 1-column. There is no JavaScript; this is all CSS.

While CSS layout systems can and should adapt to changes in their input/output, there are thresholds where the layout really needs to transform; and Media Queries allows you to do that, to take multiple designs and conditionally combine them into a single page.

So that's an overview of what's here, what's coming, when you can expect it, and why it's not here yet. :) Let's move on to how things go from idea to impelmentation at W3C, and then I want to close with how you can get involved.

How CSS Specs Grow Up

On the W3C side, a spec develops over essentially 3 stages:

  1. Working Draft, which is the design phase
  2. Candidate Recommendation, which is the testing phase
  3. Recommendation, which is the maintainance phase

In the CSSWG, we further break down the design phase into 3 sub-phases:

  1. In the Exploring stage, the spec is often incomplete, possibly changing greatly between drafts, and possibly including many features that will be dropped as the spec matures.
  2. In the Revising stage, the module is mostly complete and the scope of its functionality is well-defined, but the spec still needs several cycles of publishing, review, and revision to uncover issues and resolve them.
  3. In the Refining stage, the spec is pretty stable and almost ready for CR, but may still need some tightly-scoped changes e.g. handling last-call comments, or general minor polishing.

The CSS Working Group transitions a spec into Candidate Recommendation when it believes the specification to be complete and precise enough to be implemented, and that no further progress can be made without feedback from implementation experience. Candidate Recommendation is the W3C's testing phase, which involves testing the implementations, but is really about testing the specification: about proving that it is well-designed and precise enough to be successfully and interoperably implemented by multiple independent teams. In this phase we build a test suite and collect test results, with the goal of showing that at least two independent implementations can both pass the test suite.

We consider the spec stable once all the failures in the test suite are well-understood and are bugs that we know will get fixed, but it's not really done we get those two passes and the W3C approves the transition to Recommendation status. And then we just maintain errata.

Sources of Innovation

So, let's see where ideas come from.

There's been a lot of argument over where designs for new CSS features should come from.

Should they come from implementations.
Should they come from designers.
Should they come from the experts in the working group.
Actually nobody makes that argument, it's not controversial enough. :)

The truth is, CSS feature designs come from everywhere. And we find that this works. It's not like any of these groups has a monopoly on good ideas. And a good design has to make sense to all of them—the people who use them, the people who implement them, and the people who can notice problems with them before we spend all this effort deploying them.

In reality, most CSS specs are a mix of input from all three sources anyway.

Review & Revision

Most of the work in the standards process is not initially drafting a proposal, but in adapting the proposals in response to feedback. Specs go through multiple cycles of review and revision; this is what helps ensure that their features actually make sense and are well-designed, that they can be implemented cross-platform, and that their descriptions have enough detail to be implemented interoperably by unrelated product teams.

Getting Involved

Anyone can get involved in standards. You just have to have the desire and technical inclination to understand what's going on under to hood, and the tenacity to dig really deep into the details and implications of all the deeply technical work that goes into building a technical standard.


So since we have extra time, I'll tell you my story of how I got involved.

I started out in the web design world by learning HTML in 1998. I did it because I was bored one day, and Laura Lemay's Teach Yourself HTML4 in 24 Hours was lying around the house. When I read the introduction it was funny, so I kept reading.

By Chapter 3 or 4, I was able to create a very simple web page, and, lacking the creativity to find a different topic, I decided to make a web page about HTML.

This was, by the way, the era of Netscape 4 and MISE4. HTML4 was new. CSS was just starting to catch on. And the Mozilla Project had just launched as the open-source repository of the Netscape 5 codebase. It was exciting times.

So as I was puttering about with some of the shiny new features on the Web, I came across a bug in Netscape's layout engine. I wanted it fixed, so I reported it through Netscape's feedback form. I figured that would go nowhere, but I remembered reading an article about the Mozilla Project in PC Magazine, so I typed mozilla.com into the address bar, got redirected to mozilla.org, and landed on this.

It explained how to get the source code, where to download a pre-1.0 milestone build (which was a kind of pre-pre-pre-pre-alpha), and where to report bugs. I downloaded a build. It was painfully slow on my Pentium I, but the bug had been fixed—later, I found out, because they'd replaced the old engine with Gecko. But it supported new shiny features so I kept it around and eventually found another bug. which I reported. And it was all downhill from there.

I became volunteer bug triage for Mozilla's layout team; I'd take a report like "my website doesn't work in Mozilla", strip down the page to just the part that wasn't working, attach that to the bug, and describe what we were doing, explain what we were supposed to be doing, and point to where the spec said that. Pls fix.

But soon I started finding places where the spec didn't say what we were supposed to be doing, or it conflicted with itself, or was just obviously wrong. So I started reporting these problems to W3C on their public mailing lists, occasionally sending a proposal for how to fix that problem in the spec.

Eventually the CSSWG got tired of this and, in 2004, invited me to join the WG as an Invited Expert to help write the specs.

And that's how I got involved in Web standards!

Then two years later I graduated from college.

I'd majored in Civil Engineering, but realizing that I was too deeply involved in Mozilla's mission to let it go, and that I couldn't be a really good engineer without letting it go, I thought, well, maybe someone will pay me to do this. And HP, thankfully, did. So I became a freelance CSSWG member, writing specs and tests and the occasional Gecko bugfix for HP, Mozilla, Microsoft, and Antenna House, until Mozilla's HR department got fussy last year and insisted on making me an employee.

And that is how I landed a career.