Nicole Sullivan Talks OOCSS and Process


Nicole Sullivan (aka @stubbornella) brought Object-oriented CSS (OOCSS) to NYC last Thursday in an updated presentation on how our best practices in CSS are killing us. She was refreshingly candid and it was great to have insight into her work process with big clients.

First, some data...

Facebook was kind enough to share some data on its CSS revamp that Nicole helped with. Some stand-outs of their CSS code debt:

  • 100MB of CSS. Have to use grep; can't read it all
  • Blue brand color declared 261 times
  • 558 unique hex values
  • 6498 total color declarations

Salesforce, another of Nicole's clients, had almost 4000 padding declarations. This is evidence of a long history of tweaking the page layout and presentation. Although "ugly," one of Nicole's deliverables actually included reusable padding classes (more on that later).

(Some) CSS best practices are myths

Don't add extra elements. This is usually based on concern that HTML size is going to grow and download speeds and SEO may suffer. However, data show that the size of HTML actually decreases with OOCSS.

Just go ahead and change markup. Think of the markup as LEGO pieces you can copy paste around the site. That's your unit of re-use.

Don't add classes (classitis). If you don't just use classes, you better prepare to calculate specificity (discussed below) for every selector you write. If you limit yourself to classes and one class per selector, you can start to rely on the cascade (order selector appears in the stylesheet) which is far more intuitive.

Use descendant selectors. This has a lot of bad side effects in your stylesheet(s)

  1. Duplicate elements in selectors
  2. Can lead to duplicate key:value pairs when design changes
  3. Specificity grows fast and gets complicated to override

Instead, think "add a class to the thing you want to change." This could be a module (container), in which case it is OK to use descendant selectors, but don't use them as the differentiator (e.g. h3 vs. #sidebar h3)

Specificity points of a CSS selector

Easiest way to show this is an example:

#sidebar section h2.eyebrow:hover {
    color: red;

Inline IDs Classes Elements
  1 2 2

Concat the numbers from left to right to make the point value. In this case, 122. Each category is an order of magnitude more important. If a selector has only elements, it's going to take more than 10 (!) to override a simple class selector.

Note that pseudoclasses (e.g. :hover) count as a class for specificity points. Also, another odd one, the universal selector(*) has a value of zero.

You should never get to the thousands because inline styles are an antipattern. Speaking of antipatterns, how does !important work? It will shift this by 4 decimal places:

h3 { 
    color: blue !important;

The color style would have a specificity of 10,000. Not quite "wins over everything else." Specificity still has room to grow!

Obviously this quickly gets complicated and is what leads to OOCSS practices like simple one-class only selectors that can be combined in HTML LEGO pieces.

OOCSS, of which a short definition always escapes me, was succintly described: OOCSS focuses on selectors as your CSS architecture, instead of what happens "between the braces." (old hotness = cross browser hacking)


CSSLint (which will also hurt your feelings) was demoed. It's a node.js app and open-sourced on github. Nicole built the alrgorithm from reverse-engineering her own CSS and looking for machine-testable bad practice

And finally, some miscellaneous bits from Q&A

Attribute selectors are slow, especially the regex ones. nth-child and first-child are practical though

Nicole built "spacing classes" for clients to do their own HTML tweaking like "m-n-l" (margin north large) as well as dividers (as HTML elements rather than just classes)

When building a style guide for a client, each unit documented should be really simple. Simple pieces, complex combinations. LEGO LEGO LEGO :)

Admittedly, OOCSS requires up-front analysis of visual design to come up with the repeatable units. This isn't always a good fit with an agile project.