Category Archives: CSS

Cascading Style Sheets

Cross-Browser Debugging CSS

I was helping Laura (a developer who works with me) learn about cross-browser debugging this week, which got me excited to share my process.

The first principal is simply:

Work with CSS, not against it.

CSS has an underlying design and when you work with it, with the natural flow of how CSS is meant to be used, you will find you have a lot less bugs. I learned CSS by reading the W3C specifications, which is why I began coding according to the language’s design, but however you learned it, you can pick up some of the key points involved.

The first thing I do is code to a good browser from the start. Our choice is Google Chrome, mainly because of the superior developer tools. When I have something working in Chrome and I am satisfied with it, I take a look at it in either Safari or Firefox.

If there is a discrepancy between these good browsers, chances are you are working against CSS. Do not try to hack around discrepancies between good browsers. Your goal is to figure out *why* it is being interpreted differently. Usually there is a very good reason. These are some of the things I check on if I have bugs:

  • HTML interpretation – did you forget to close a tag? Did you wrap an inline element around a block level element? Anything that veers off the standard will be interpreted differently by different browsers.
  • Run your CSS through CSS lint. It will give you a good sense of any errors (missing semi colon?) that might be throwing you off. For debugging cross browser differences, the errors are more interesting than the warnings.
  • Forgot to use a reset/normalize stylesheet and are relying on (different) browser default styles.
  • Browser support differences. Are you using advanced CSS3 properties or HTML5 elements? Check browser support to be sure all your target browsers are covered (quirksmode is where I usually do this). If not, you may still be able to use the fancy-pants properties, you’ll just need to design clever fall-backs for the clunkier browsers. For example, borders instead of drop shadows or square instead of rounded.
  • Margins are not being trapped correctly. If you have weird spaces in unexpected places, chances are your margins are collapsing in an undesirable way.
  • You created a new formatting context in one browser, but not in another. Typically this happens as a result of overzealous use of the zoom:1 property to trigger hasLayout in IE. Yes, hasLayout is essentially the same thing as a new formatting context in better browsers.
  • Using absolute position, without setting horizontal and vertical offset. For that reason, the absolutely positioned element will have the same position it would have had when set statically. However, if you try to manipulate the top, right, bottom, or left values, the element will all of the sudden be positioned relative to the nearest relatively positioned ancestor causing it to jump.
  • Did you combine display types in unexpected ways? For example, the spec doesn’t lay out what happens when a table-cell is next to a floated element without a table row or table in between. It doesn’t mean you can’t do it, but it does mean that if you do, you open yourself up to potential bugs and will need to spend more time cross browser testing.
  • Is whitespace affecting your layout? You almost never want to have whitespace dependencies on your CSS display, but sometimes it happens, particularly with display inline and inline block and with images since they look like blocks, but, unless you set them all to display block, don’t behave that way.
  • Rounding errors can cause display differences. All flexible layouts and grids have to deal with sub-pixel rounding errors, they each find different ways to minimize the visibility of these differences.

If you don’t read anything else, read the next two paragraphs

The most important thing to keep in mind is that error behavior is not defined in the spec. If you go off-roading you don’t know what you will get. Chances are it will be different between browsers. If you are combining odd properties (like margins on an inline element), you will have cross browser differences.


I think of CSS like a choose your own adventure. When you have made certain choices, others become obvious. For example, you need to first choose your display type block, inline, inline-block, table. When you have chosen that, you are left with a tool-box of appropriate tools to use to alter the display. For example,

  • Block level elements should be used with margins, paddings, height and width. Line-height isn’t appropriate.
  • Inline elements have line-height, vertical align, and can also be whitespace sensitive. Margins, paddings, heights, and widths aren’t appropriate.
  • Tables have vertical and horizontal alignment and can sometimes behave bizarrely if you have one element of a table without the others (e.g. a table-row with no table-cell). Margins are inappropriate for table-rows and table-cells. Padding is inappropriate for tables and table rows.

If you stick to the tool box that naturally goes with your display type, you will have far fewer bugs and cross-browser differences.


Next, if you chose block, you must choose your positioning mechanism. (The others are generally positioned according to the normal flow). So for blocks you can choose:

  • Float – brings blocks all the way to the right or left. If you floated something, you made it a block level element, which means previously applied vertical-align or line-height properties may no longer work.
  • Absolute – positions the element relative to it’s nearest position relative ancestor. Keep in mind that absolutely positioned elements do not trigger reflows and are not reflowed when ancestors and siblings are changed. This is a strength for animations, but can cause display issues if you use too much position absolute with dynamically updating content. (e.g. the old-school example is corners that do not move when more content is added to the box).
  • Static – the default, this is how you get back to a standard element in the normal flow.
  • Fixed – positions the block relative to the viewport. Rarely used.
  • Relative – mostly doesn’t affect the node it is applied to, but children will get their absolute position relative to this node.

I’m not organized enough to enumerate all the display and positioning types and tell you which can be used/not used with which other properties, so you are going to have to think it through for yourself when debugging and writing code. There are two important things to consider:

  1. Do these properties go with the display and positioning types I have chosen?
  2. Do sibling positioning types go together?

For example, does it make sense to have a float, table-cell, and inline element interacting with each other? What should the browser do with that? Is it defined in the spec? If not, you are probably going against the grain of CSS. That can be ok sometimes, but you should know exactly why you chose to do it and leave extra time for cross browser testing.

Internet Explorer

When you have resolved all the discrepancies between the good browsers, you are ready to look at IE. I recommend starting with the oldest version of IE that you need to support because lots of bugs continue to exist in newer versions (in slightly modified form) so you will have less to fix if you start with the worst one.

Even with IE, you want to try to figure out why it is interpreting something differently rather than just hack around it. Adding * and _ hacks to your code willy-nilly is like finding out a function is returning the wrong value (say four less than it should be) and just adding the difference to it rather than figuring out where the math went wrong in the first place.

return result+4;

That said, it is ok and sometimes necessary to hack IE6 & 7. IE8 usually only needs hacks to accomodate a lack of support for modern CSS3. If you think you need to hack, try to figure out the exact bug you are dealing with. There are tons of resources for this online (anyone remember PIE?). The particular problems which require hacks in IE6 & 7 are:

  • Needing to add hasLayout with zoom:1
  • Position relative causing things to disappear
  • 3px float bug
  • Expanding container float bug (useful!) and overflow hidden which unfortunately “fixes” this useful bug.
  • Do you have a favorite IE bug? I’d love to hear about it in the comments.

There are, of course others, but these are the few I’ve had to hack around for OOCSS. The others occur far less frequently, like the duplicated content bug when you have two floated elements with a comment in between. I don’t know how to explain figuring out IE bugs because, for the most part, I’ve internalized them. Like speaking a foreign language. The best I can suggest is to carefully examine what you can see and carefully craft your google search to describe it. Don’t start hacking until you identify the bug. The dev tools for IE are horrible, so you may need to use background colors to “see” the problems. I create debug stylesheets for that purpose.

Implementing solutions

When you have figured out what is wrong and you know how to solve it, you are ready to figure out how to put it in your code without breaking everything. Here is my process:

  1. Rely on the cascade
  2. Use vendor prefixes
  3. Use * and _ hacks for IE6 & 7
  4. Almost never use \9 for IE8
  5. Know when to quit trying to hack IE
  6. Never use hacks to target the latest versions of Firefox, Chrome, or Safari.

That’s a lot to take in, so I’ll detail each one below.

Rely on the Cascade

First, rely on the cascade whenever possible. CSS has a natural system of fallbacks built right in. Browsers take into account the last value that they were able to understand (this is how the cascade was designed to work). This means that if you order different solutions to the same problem from least advanced to most advanced, browsers will naturally use the most advanced solution they are capable of understanding. For example:

  background-color: #ccc; /* older browsers will use this */
  background-color: rgba(0,0,0,0.2); /* browsers that understand rgba will use this */

Use vendor prefixes

The next tool you want to employ is vendor prefixes. They allow you to give different values to different browsers, particularly for properties that haven’t stabilized.

background: #1e5799; /* Old browsers */
background: -moz-linear-gradient(top, #1e5799 0%, #2989d8 50%, #207cca 51%, #7db9e8 100%); /* FF3.6+ */
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#1e5799), color-stop(50%,#2989d8), color-stop(51%,#207cca), color-stop(100%,#7db9e8)); /* Chrome,Safari4+ */
background: -webkit-linear-gradient(top, #1e5799 0%,#2989d8 50%,#207cca 51%,#7db9e8 100%); /* Chrome10+,Safari5.1+ */
background: -o-linear-gradient(top, #1e5799 0%,#2989d8 50%,#207cca 51%,#7db9e8 100%); /* Opera 11.10+ */
background: -ms-linear-gradient(top, #1e5799 0%,#2989d8 50%,#207cca 51%,#7db9e8 100%); /* IE10+ */
background: linear-gradient(top, #1e5799 0%,#2989d8 50%,#207cca 51%,#7db9e8 100%); /* W3C */

Notice the two syntaxes for webkit. Just like normal property fallbacks, vendor prefixes should be ordered from oldest version to newest so that each browser gets the best code it is capable of handling.

If there is a standard syntax, you want to put that last so that as support for the standard increases, more and more browsers will use the best code. This is marked with a comment “W3C” in the above code.

Use * and _ hacks for IE6 & 7

When you have identified specific IE bugs, and you know how you want to work around them, use _ and * hacks to target that particular browser. For example:

.clearfix {
  overflow: hidden; /* new formatting context in better browsers */
  *overflow: visible; /* protect IE7 and older from the overflow property */
  *zoom: 1; /* give IE hasLayout, a new formatting context equivalent */

All IE hacks target a particular browser and everything before it, so for example:

  • _ targets IE6 and older
  • * targets IE7 and older, and
  • \9 targets IE8 and older UPDATE: IE9 is also targeted for certain properties.

That means that when you use multiple hacks you need to put them in order; underscore, then star, then \9.

Almost never use \9 for IE8

That said, I have not really needed to use \9 for any browser quirks in IE8. I use it simply to fill in the gaps when there is a difference in support. For example, if I’m using a box-shadow in better browsers, and the box looks weird without anything around it in IE8, I’ll use \9 to add a border for that browser. The cascading technique wouldn’t work in this case, because the backup method is applied to a different property.

Know when to quit trying to hack IE

Don’t try to make everything exactly the same in IE. It is important to think about what is in the best interest of each set of users. Do you waste another several HTTP requests, extra HTML, JS, and additional CSS to force rounded corners to work in IE6-8? For me, the answer is a clear “No.”

It is important to know when to give up on a particular feature. For example, don’t use filters to simulate css3 gradients. They cause performance issues and layout bugs. It is best to avoid the desire to make your site exactly the same in every single browser regardless of capability. Users of IE 6-8 are much better off with a simplified experience (not broken, just simpler) that with a site that rolls out all the bells and whistles using a ton of polyfills, but is incredibly slow.

For example, avoid the following code to duplicate the gradient from the example above.

filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#1e5799', endColorstr='#7db9e8',GradientType=0 ); /* IE6-9 */

Never use hacks to target the latest versions of Firefox, Chrome, or Safari.

Finally, if you think you need to hack to serve different code to Firefox, Chrome, or Safari — something has gone very awry. It makes sense to go back and look at what you’ve written to see if you are going against the grain of CSS.

Do you have particular techniques for debugging CSS? Or for implementing fixes once you’ve found a solution? I’d love to hear more about it in the comments.

If you would like to read this post in spanish, click here.

Code formatting for CSS Gradients

I may have found a way to format CSS3 Gradients that doesn’t make my eyes bleed. Yippee!

I was talking to @glan the other day about CSS3 gradients. We were discussing how to break them down into understandable layers and the difficulties when things you need to know about may be split across multiple properties. At the same time, I was checking out these cool CSS Coding Standards shared by @csswizardry, and I started wondering if formatting the code for CSS gradients could make them easier to understand.

I grabbed one of Lea Verou’s CSS3 gradient patterns as a starting point. They are insane and amazing and mind blowing. If you haven’t checked them out, you totally should. Anyway, I grabbed the code from the arrows example to try out different formatting options.

Option A – One line per property value pair

Let’s start off with the standard one line per property value pair.

.arrows {
	background: linear-gradient(45deg, #92baac 45px, transparent 45px), linear-gradient(45deg, #92baac 45px, transparent 45px)64px 64px, linear-gradient(225deg, transparent 46px, #e1ebbd 46px, #e1ebbd 91px, transparent 91px), linear-gradient(-45deg, #92baac 23px, transparent 23px, transparent 68px,#92baac 68px,#92baac 113px,transparent 113px,transparent 158px,#92baac 158px);
	background-size: 128px 128px;

Ok, awful, right?

Option B – Line return for each gradient

Let’s try adding a line return for each linear gradient.

.arrows {
	linear-gradient(45deg, #92baac 45px, transparent 45px), 
	linear-gradient(45deg, #92baac 45px, transparent 45px)64px 64px, 
	linear-gradient(225deg, transparent 46px, #e1ebbd 46px, #e1ebbd 91px, transparent 91px), 
	linear-gradient(-45deg, #92baac 23px, transparent 23px, transparent 68px,#92baac 68px,#92baac 113px,transparent 113px,transparent 158px,#92baac 158px);
	background-size: 128px 128px;

Option C – Tab per value

The last example was better, but I could kind of see a pattern in it, so next, I tried formatting it like a table with tabs to separate the columns.

.arrows {
	linear-gradient(45deg,	#92baac		45px,	transparent	45px), 
	linear-gradient(45deg,	#92baac		45px,	transparent	45px)	64px		64px, 
	linear-gradient(225deg,	transparent	46px,	#e1ebbd		46px,	#e1ebbd		91px,	transparent	91px), 
	linear-gradient(-45deg,	#92baac 	23px,	transparent	23px,	transparent	68px,	#92baac 	68px,	#92baac	113px,	transparent	113px,	transparent	158px,	#92baac	158px);
	background-color: #e1ebbd;
	background-size: 128px 128px;

I wanted to like this option, I really did, but you have things lining up that aren’t the same kind of values and that feels weird.

Option D – Line return per color stop

So next, I thought I’d try adding a line return at every comma (thus every color stop).

.arrows {
			#92baac 45px, 
			transparent 45px
			#92baac 45px, 
			transparent 45px
		) 64px 64px, 
			transparent 46px, 
			#e1ebbd 46px, 
			#e1ebbd 91px, 
			transparent 91px
			#92baac 23px, 
			transparent 23px, 
			transparent 68px,
			#92baac 68px,
			#92baac 113px,
			transparent 113px,
			transparent 158px,
			#92baac 158px
	background-size: 128px 128px;

Usually I write in a quite compressed style, but I find myself preferring to look at Option D.

What do you think? Would you vote for A, B, C, or D? Do you have a different way of formatting that works well for you?

UPDATE: Don’t forget to add a pre tag around your example code if you include it in the comments.

Scope donuts

Note: This article is esoteric-could-be-should-be wishing for future browsers. If you only like to hear about what you can use right now, you won’t like this. You’ve been warned. ;)

At first, when the HTML5 working group added the scope attribute I was skeptical. I thought, “oh dear, this is going to be another way for developers to cause massive duplication and inconsistency.” I still do worry, but I’m more excited about the tool and hoping we can also find really great things to do with it.

Scope is great for mashups

The first that comes to mind, and the reason it was created, is mashups. Imagine you want to pull in a twitter feed or a video into your page. Unless you intend to rewrite it all (and often widgets block such fine grained control), you’ll probably be allowing someone else’s CSS onto your page. That can be daunting to say the least.

For example, the twitter widget I use pulls in ~1.36kb of CSS that could potentially interfere with my site styles — and it does it via JavaScript, so unless I’m ready to switch to using the API rather than a widget, I’m stuck allowing their styles on my page.

The way to sandbox those styles today is to be sure each style starts with a twitter specific class name. You can see from their code that they did a very good job of it. None of their styles will be polluting mine. Unfortunately, not all widget CSS will be so enlightened (especially not ad code). HTML5 offers another option for allowing authors to sandbox styles called the scope attribute. David Storey has a much better explaination of scope on his blog, I’ve adapted this example from his:

  <style scoped>
    p { color: blue; }
  <p>The text in this paragraph will be blue</p>
  <p>And in this paragraph too</p>
<p>This paragraph is out of scope so will be gray</p>

If your browser supports it, it will look like this:

The text in this paragraph will be blue

And in this paragraph too

This paragraph is out of scope so will be gray

There are a lot of really great use cases for this, widgets, ads, even large companies with multiple teams putting functionality on a single page. On the other hand, there is a use case for which it falls flat: components. I’d love to see it extended so it could work for both.

Scope is more than a starting point, it’s a donut

Donuts by mamaloco

The interesting thing about UI components (different than ads or widgets) is that they can sometimes contain other unrelated components. You can have a tabset that contains headings, paragraphs, media blocks, or even (holy ugly!) another tabset. Ideally, you would scope the CSS of the tabset to the tabs only, so it can’t bleed outward and change styles on the rest of the page, but you also want to prevent the styles from bleeding inward to content components. So we need a way of saying, not only where scope starts, but where it ends. Thus, the scope donut. The styles affect the donut shape, but not the other components which can be found in the donut hole.

Tabs from the admin section of Let's Freckle, a time tracking app.
Figure 1: Tabs from Let’s Freckle, a time tracking software.

It has always struck me as odd that scope is declared in the HTML, because ideally with reusable components you wouldn’t want to repeat that code all over the place. Each of the tabs has different content related to my Freckle settings. The content styles aren’t specific to the tabs, but may also be used in other parts of the page. We want to make that reuse possible, by keeping our tabs from affecting the way content (the components in the donut hole) components look. I’d like to do this once, in the CSS, and then have it apply anywhere the component is used.

The first step is to be able to define that component, including both it’s HTML and CSS. Let’s start with a basic box. It’s HTML might look something like this:

<div class="box tabs"> 
    <div class="hd">
    	  Box Header
    <div class="bd">
        Box Body

The scope of a box begins at the wrapper div with the class box, and ends at the box body. We don’t for example want the styles on the box spilling over into whatever content we put in the box. I’m not sure how exactly to say this in CSS, but I like the idea that using nested selectors implies meaning about the relationship of those parts. e.g. nesting the selectors means that the sub nodes belong to the same component.

In other words, if I applied a text color to my box, it would change the color of text in the header, but not to subnodes in the body. Let’s take a look at an example syntax. I don’t really know what the right syntax is, but I’m more and more convinced it is worth finding a syntax to express it.

.box {
    border: 1px solid gray;
    color: red; // would cause text in the header to be red, but not inside the body.
    scope: start; 
    & .hd {
        border-bottom: 1px solid gray;
    & .bd {
        scope: end;

This basically says that hd and bd belong to the box object and that the scope of these styles starts at .box and ends at .bd. It prevents styles from bleeding either up or down. Note: I do wonder if we need to say where it starts given that the nature of CSS is that it is namespaced to wherever the selector begins. It also makes me wonder why in the world scope is in the HTML rather than the CSS. It seems oddly out of place. Moving on…

There are several ways to mark up tabs, but let’s assume the HTML of the tabs component looks like this:

<div class="box tabs"> 
    <div class="hd">
        <ul class="tabControl">
            <li><a href="#">Personal</a></li>
            <li><a href="#">Date & Time</a></li>
            <li class="current"><a href="#">Password</a></li>
            <li><a href="#">API</a></li>
            <li><a href="#">Timer</a></li>
            <li><a href="#">Rounding</a></li>
    <div class="bd">
            <li class="tab-bd">Tab 1 Content</li>
            <li class="tab-bd">Tab 2 Content</li>
            <li class="tab-bd current">Tab 3 Content</li>
            <li class="tab-bd">Tab 4 Content</li>
            <li class="tab-bd">Tab 5 Content</li>
            <li class="tab-bd">Tab 6 Content</li>

What you can see is that tabs are an extension of an ordinary box. They have a head and body wrapped in a div with the classes box and tabs. What makes the tabs unique is that both the head and body are filled with unordered lists which correspond to the tab control and tab body respectively.

Tabs with the donut highlighted
Figure 2: Tabs with the donut highlighted. We don’t want any styles falling either into the donut hole. This where scope ends. (See? It’s donut colored! Forgive me, this diagram is very very ugly.)

We could try to express the next bit by combining three tools:

  • nesting for defining the component structure,
  • extends so we don’t need to repeat anything we already know about boxes in the code for tabs, and
  • a new property “scope” which tells the browser where to stop allowing styles to bleed down.
.tab {
    extends: .box; // so inherits the starting scope 
    & .tab-bd {
        scope: end;

So, any styles for tabs should only apply to the nodes between the start and end of scope, or between .box and .tab-bd. Is this the right syntax? I’m not sure actually, but I tend to like it.

The region we want to apply styles to.
Figure 3: the region we want styles to apply to.

Figure 3 sums up what I’m asking for — a way to apply styles only to the divs which make up my object and not to content that simply happens to be inside it. You can do that today with careful use of style and the child selector “>”, but in a world where some content is trusted more than other content, it might be easier to just be able to say explicitly which donut of elements I want a particular set of styles to apply to.

You may have heard the Henry Ford quote:

If I’d asked customers what they wanted, they would have said “a faster horse”.

Henry Ford

I think lots of us want *way* more than just a faster horse. :)

What do you think? Useful? I’ve been holding on to this post for four months because I wasn’t sure about it, because it is quite different from how things work now, but I thought I’d put it out there and see what other people think.

Don’t Style Headings Using HTML5 Sections

Styling headings is either a deceptively complex problem, or maybe the design of CSS made it appear complex when it need not have done.

When styling headings (or really anything) we want three big goals to be met:

  1. DRY – Do not repeat yourself. We want to set headings once and never (ok, rarely!) repeat those font styles or selectors. This will make our site easier to maintain.
  2. Predictable – The heading should look the same no matter where on the page it is placed. This will make creating new pages and content easier.
  3. Keep specificity low and selectors as simple as possible. This will help with performance and keep the site from growing more and more tangled over time.

The html5 section tag is weird. It dramatically changes the way we use headings. It also changes the way browsers and assistive technologies are meant to interpret those headings. The spec says:

“The section element represents a generic section of a document or application. A section, in this context, is a thematic grouping of content, typically with a heading.”
The HTML5 Spec

The spec goes on to warn us that sections are not really meant to be used just because you want to attach a style a particular piece of content:

“The section element is not a generic container element. When an element is needed for styling purposes or as a convenience for scripting, authors are encouraged to use the div element instead. A general rule is that the section element is appropriate only if the element’s contents would be listed explicitly in the document’s outline.”
The HTML5 Spec

People seem to have blocked out this last (very important) bit, so I’ll reiterate. Sections aren’t really meant to be used by CSS for style purposes (at least not *only* for styles). So, if sections aren’t meant to be used to make my headings purty, why do they exist? They change the way the browser and assistive technologies interpret the importance of a heading relative to the other headings on the page. To understand this, you need to know a bit about the pitfalls of the way headings have been written up until now.

HTML Headings

Think back to the outlines you wrote for term papers in high school. Each bit of a website is meant to be like that, each heading corresponds to a piece of that outline, and you know when you go up or down a level by the heading level chosen. H2 is down one level from H1. And h6 is down four levels from H2.

I. Big roman numerals are the H2s
   A. This is an h3
   B. This is also and h3
      i. Now we have an h4
      ii. And another h4
II. Big roman numerals are the H2s
III. Big roman numerals are the H2s
IV. Big roman numerals are the H2s

The trouble is, on a modern website or web app, this model isn’t a really natural fit. Especially if a site “mashes up” content from sources they don’t control (say for example adding a twitter feed to a blog), they may not be able to set the heading levels used by the mashup content. In this case, most developers, just include the new content, and the outline gets a little murkier.

A murky outline may be somewhat normal, because I’d take it a step further and say that, on most modern websites, the idea that the site has much in common with a high school term paper outline is a bit of a stretch — The section element tries to bridge the gap between the w3c’s outline view of the web and the way developers are really building sites. The section element essentially reorders the heading tree so that whatever headings are used, if they are wrapped in a section element, they will be made to fit in with other content on the page. They need only be internally consistent within each section.

<h2>Me on the web...</h2>
<h1>My Twitter Feed</h1>
<ul class="tweets">
 <li>Mmmm, cornflakes.</li>
 <li>Something inane...</li> 
<p><a href="more.html">More stuff on the web</a></p>

HTML5 Headings & Section Elements

If you wrap it in a section, the browser will interpret it as one level down from it’s parent heading.

<h2>Me on the web...</h2>
<h1>My Twitter Feed</h1>
<ul class="tweets">
 <li>Mmmm, cornflakes.</li>
 <li>Something inane...</li> 
<p><a href="more.html">More stuff on the web</a></p>

The section element also makes it clear that the list of tweets belongs to the Twitter feed, and the more link does not. This makes content more portable, which is okay — even if it maybe isn’t that important. However, it does seem to be confusing people about how they should style their headings. I think this bit of the spec might be confusing people:

Notice how the use of section means that the author can use h1 elements throughout, without having to worry about whether a particular section is at the top level, the second level, the third level, and so on.
The HTML5 Spec

This has lead people to think that they should only ever use h1s (which, is a fair interpretation of the working group’s note). However, lots of people have taken it a little too far because they didn’t read the second quote [1], where it says additional section elements shouldn’t really be used only to apply CSS styles. Admittedly a subtle difference, but important! Section elements are meant to help the browser figure out what level the heading really is, but not necessarily to decide how to style it. By tying styles to browser heading level interpretation, developers (trying to implement html5 from the spec) are ending up with selectors that look like this:

h1{font-size: 36px}
section h1{font-size: 28px}
section section h1{font-size: 22px}
section section section h1{font-size: 18px}
section section section section h1{font-size: 16px}
section section section section section h1{font-size: 14px}
section section section section section section h1{font-size: 13px}
section section section section section section section h1{font-size: 11px}

(Note: This is vastly simplified as I’ve only included sections and not the other sectioning elements like articles or asides. This is a more realistic, real life code sample.)

Let’s see how well this meets our goals:

Q: What if, semantically speaking, you need to add an additional section to a bit of html?

It will unintentionally change the way your headings look. If it is high enough on the document tree it could change your entire page. That seems badly unpredictable.

Q: What happens if the design calls for a 14px heading in a part of the site that is only nested two sectioning contents deep?

To make it work with the existing code, you would need to add additional unnecessary section elements. The spec pretty clearly states that section elements are not meant to be added just to change styles. Plus, that is just kind of gross.

Q: What if we create another rule that duplicates the 14px property value pair?

section.special section h1 {font-size:14px}

This clearly isn’t DRY. We’re repeating the code to set the font-size to 14px, and our specificity is starting to get weird. If we want a normal two-section deep heading (22px) we now can’t have it in the special section. We also can’t reuse the new rule anywhere else. Continue in this direction for a while on a project and you can end up with hundreds or even thousands of heading declarations. Eek! This isn’t meeting our stated goals at all.

(For more info about how this can get out of control, check out this video on how our current methods for styling headings are leading to bad outcomes.)

So, how do we style headings in an HTML5 world?

The answer is right there in the spec, next to the place where we learned to use only H1s. We shouldn’t use sectioning elements for styling. We should let them do the job they were designed for, which is sorting out the document tree, and solve styling issues another way that meets our goals better: with simple reusable class names that can be applied to any of our headings no matter how deep they may be in the sectioning content.

I recommend abstracting site wide headings into classes because then they are portable, predictable, and dry. You can call them anything you like. Jeremy Keith recommends something like:

.Alpha {}
.Beta {} 
.Gamma {} 
.Delta {} 
.Epsilon {} 
.Zeta {} 


.tera {} 
.giga {} 
.mega {} 
.kilo {} 
.hecto {} 
.deca {} 
.deci {} 
.centi {} 
.milli {} 
.micro {} 
.nano {} 
.pico {} 

I keep it simple with:


It doesn’t really matter what system you choose as long as it is something easy for your team to remember. Then, no matter how many section levels deep your heading is nested, you can make it look just how you want:

<h1 class="giga">Me on the web...</h1>
  <h1 class="kilo">My Twitter Feed</h1>
  <ul class="tweets">
    <li>Mmmm, cornflakes.</li>
    <li>Something inane...</li>
<p><a href="more.html">More stuff on the web</a></p>

So now, your twitter feed, from the previous example, can be in the sidebar on an article page, or in the footer of your homepage, and it will still look the way it was designed to. Whether you are using html5 sections or not, you don’t want to repeat code or have it be unpredictable, so I think separating styles from how the browser generates the page outline is just sensible.

UPDATE 9/6: If you truly cannot change the HTML, even to add class names, then the only way to style that bit is to put a wrapper around it with a unique class and use descendent selectors to force the style you want. This should be the exception, not the rule! (Thanks Simon for pointing out that I wasn’t addressing one of the use cases I had talked about above)

<h1 class="giga">Me on the web...</h1>
<section class="tweetfeed">
  <h1>My Twitter Feed</h1>
  <ul class="tweets">
    <li>Mmmm, cornflakes.</li>
    <li>Something inane...</li>
<p><a href="more.html">More stuff on the web</a></p>

If you would like a far more eloquent walk through all the new html5 elements, get Jeremy Keith’s book HTML5 For Web Designers.

Thanks to Alex Kessinger and Josh for helping me solidify my thoughts around this by bringing up good questions on the CSS Lint Google Group.

CSS Lint open sourced

Nicholas Zakas and I spoke at Velocity a few minutes ago. First we talked about CSS 3 and it’s impact on performance, then we demoed and open sourced CSS Lint! I really couldn’t be more excited (or relieved, I was super duper nervous before this presentation).

CSS Lint is a tool to help point out problems with your CSS code. It does basic syntax checking as well as applying a set of rules to the code that look for problematic patterns or signs of inefficiency. The rules are all pluggable, so you can easily write your own or omit ones you don’t want.

Rules currently tested

  • Parsing errors should be fixed
  • Don’t use adjoining classes
  • Remove empty rules
  • Use correct properties for a display
  • Don’t use too many floats
  • Don’t use too many web fonts
  • Don’t use too may font-size declarations
  • Don’t use IDs in selectors
  • Don’t qualify headings
  • Heading elements should have a consistent appearance across a site.
  • Heading styles should only be defined once
  • Be careful using width: 100%
  • Zero values don’t need units
  • Vendor prefixed properties should also have the standard
  • CSS gradients require all browser prefixes
  • Avoid selectors that look like regular expressions
  • Beware of broken box models

(We’ll allow you to turn off rules that hurt your feelings soon!)


Many people have expressed an interest in contributing to the CSS Lint project. We were waiting to have a solid plugable architecture and API before taking contributions. The exciting news is that we are now ready! There are several ways you can contribute:

  1. If you are comfortable with CSS, submit rule ideas. You must provide the rule name, a human readable explanation, browsers affected, and a test case.
  2. If you are comfortable in JavaScript, fork the github project, code up a rule, and submit a pull request. You’ll need to provide all the same documentation requsted in item 1.
  3. If you are comfortable with Node, test out the command line version, submit feature requests.

CSS Lint for Node.js

If you’d like a command line version of CSS Lint, you can install CSS Lint for Node.js using npm using the following:

sudo npm install -g csslint

Once installed, you can pass in any number of CSS files or directories containing CSS files to see the results. For example:

csslint test.css dir_of_css/ test2.css

You’ll receive the same errors and warnings as you would with the web interface.