Happy with your CSS files in your big app?


Hello, my name is Albino Tonnina.
I’m a senior front-end developer at Workshare, London.

I work daily with a bunch of talented people. Young developers and people who remember how to write the Box Model Hack for IE6.

Javascript aces and CSS ninjas.

Working with CSS can be a dirty frustrating job…

Through the years I read and worked with these acronymic CSS methodologies that came out of some brilliant minds in an admirable attempt to end up the mess, fighting against the many specificity issues or the globally scoped nature of CSS, trying to figure out how to maintain a large codebase, the hacks etc.

…working with CSS in a large scale project can be an amazingly dirty frustrating job.

I eventually realized that the level of comfortability with markup and styles can differ from developer to developer. You love it, hate it or everything in between, it may be the best or the worst part of your job. Right?

We need a methodology

So we don’t mess things up!

What are we trying to solve here? Here’s my list, in order of importance:

  • Have a better Developer Experience.
  • Work with a low-maintenance environment.
  • Easy elimination of unused (dead) CSS code.
  • Forget about specificity issues, hacks to cover hacks etc.
  • Face the lack of the concept of local scope in CSS.

So which one we want to adopt?

SMACSS, OOCSS, BEM, ITCSS, BEMIT, Atomic CSS? Abstract as much as you can? Get a rigid naming convention? Build the interface in reusable pieces? Let me share with you my slightly biased thoughts about these popular methodologies and finally the newcomer: Bandit.



  • Separate container from content: big no to location-dependent styles.
    An object should look the same no matter where you put it. You should not mimic the structure of your markup in your CSS file.
  • Separate skin from structure: Structure and positioning should be kept separated from visual features (color, background, border). Use extender classes to add this visual features.

My thoughts

OOCSS is all about abstraction and reusability. Styles are managed like Lego pieces that you mix in your markup. That should give you smaller files, reduce duplication and keep everything easy to maintain.

Also OOCSS has this nice concept of the performance freebies: every time you reuse something in your CSS, you’re essentially creating new styled elements with zero lines of CSS code. Sounds great.

Why I’m not adopting it

written by Mark No-More-Here, designed by Joan Long-Gone

With companies, developers come and go. This could be potentially dangerous for the stability of an architecture such as OOCSS. My fear is that it relies too much on the assumption that every developer in the company is at the same level of experience and dedication.

In the previous example, some of the styles are almost set inline (.left-pad-16), while maybe some are hidden in some CSS files located in a big ../styles/ subfolder of the project. This could lead to a bad DX if the codebase is not religiously maintained.

Dilemma: what if I really really need a .left-pad-15 class that still doesn’t exist, do I add it or I override only the styles of the tag that needs it, just this time? In my experience developers tend to do both, depending on the moment, the discipline, the hurry, how much they care.

Also, what about breakpoints and Responsive Web Design? What if that tag needs to be styled differently in a small breakpoint? It may look like this?

What about specificity now? Good luck maintaining this code.

If there are rules to break, developers will break them.

More about OOCSS


Block, Element, Modifier

BEM may be defined as a concrete application of OOCSS. It tries to address the naming issue by suggesting a structured way of naming classes, based on properties.

My thoughts

BEM, the architecture of OOCSS with a strict set of recognizable naming rules.

This set of rules works very well. It helps to write better markup, it forces you to think in blocks, which is good when you want to modularize in your projects. It promotes a flat hierarchy of selectors, which is good when you have to deal with specificity issues. Also, I think that BEM it is very good when we need to prototype fast.

Why I’m not adopting it

What I said about OOCSS applies here too. 
And I’m sorry, but when I see production code written using the BEM naming convention I don’t like to read it. And I love to write HTML templates and SASS files! I think this is bad readability, hence not great DX. 
May I suggest also steep learning curve? 
Finally, abstracting may be hard sometimes, for example you may end up abusing descendant selectors trying to maintain reusability:

More about BEM


Scalable and Modular Architecture for CSS

Like OOCSS, this is a well known approach to modular CSS. 
They both share the same goal: help people write flexible and maintainable CSS.

SMACSS Categorization

This is the very core of SMACSS. This methodology asks developers to shift from a page mentality to a pattern mentality. Pages become compositions of modules. Think about SMACSS as a style guide, more than a rigid framework.
The categorization scheme offered by SMACSS is the following:

  • Base: for defaults (html, body, etc) and resets
  • Layout: for page sections
  • Module: for modular reusable elements
  • States: for element variations (active, inactive, pressed etc)
  • Theme: color schemes, typography etc.

The purpose of this categorization: less code repetition, a more consistent experience, and easier maintenance.


  1. Increase the semantic value of a section of HTML and content with the new HTML5 tags: section, aside, header, footer etc. .
  2. Decrease the expectation of a specific HTML structure avoiding tag selectors.

What I didn’t like

  • Difficult to qualify styles — what category? In a fast producing multi developer environment this could lead to conflicts in the codebase.
  • CSS may be too detached from the markup, will we delete the classes that we don’t need anymore or we will keep bloating those theme files? The risk is to carry too much unused code around?

More about SMACSS


Inverted Triangle CSS

Here’s another approach to help us fixing the mess :)

The Principle

Separates CSS codebase into layers.

Similarly to SMACSS, ITCSS provides a categorization scheme for your CSS files.

From top to bottom:

  • Settings: variables. Font, colors definitions, etc. No output.
  • Tools: mixins and functions. No output.
  • Generic: reset and/or normalize styles.
  • Elements: bare HTML elements (like H1, A, etc.).
  • Objects: class selectors which define undecorated design patterns, like the media object from OOCSS.
  • Components: specific UI components. Majority of code.
  • Trumps: utilities and helper classes with ability to override anything.

My thoughts

I like this methodology, I like SMACSS too. I see ITCSS sharing the same merits and faults of SMACSS.

By the way, you can mix these approaches as much as you like! 
Be cautious though.

That’s all I have to say about ITCSS, I guess this article is getting a little long and I still have to start talking about Bandit :)

More about ITCSS

Other methodologies

There is BEMIT that tries to address issues of BEM, like the lack of support for RWD and the readability issues by adding categorized namespaces, like
c- for Components, o- for Objects, u- for Utilities, and is-/has- for States.

More about BEMIT

There is also another approach called Atomic Cascading Style Sheets that is all about mapping classes to a single style, like so:

Read about Atomic CSS on Smashing Magazine

We sure have enough methodologies to choose from!

Short answer is no.

I like all these approaches and yet I’m not completely happy with any of them. Over the years I sometimes found myself stuck between the apparent need to break the rules of this or that methodology opposed to the frustrating feeling of adding dirtiness to my initially clean and tidy files.

Of course, if you are working alone on a project that won’t likely evolve over time you could just choose not to worry about naming conventions, abstractions and organization of files.

On the other hand if you are working on a constantly mutating large project manipulated by many developers over time, the need of a set of principles, rules and best practices to follow is strongly needed.

Introducing Bandit.

A methodology to write highly modular and scalable CSS in a modular and scalable application

Bandit It’s not something completely new

It steals ideas from the other great methodologies.

Problems Bandit wants to address

  • Have a low-maintenance environment
  • Solve issues with multi developer environments
  • Dead easy dead code elimination
  • Have a Smooth DX, visual order, simplicity.

Does Bandit fit in our project?

I’m assuming you are working with a modular application, using tools like Backbone/Marionette/Angular/React/Ember.
Better if you manage to require your css files together with your views at render time, there are ways to achieve that.

Files Organization in Bandit

All the files that create a module are contained within a folder.
Styles go away when module goes away (dead code elimination).
Also this structure is great if you want to load CSS asynchronously
Can work in React, Backbone/Marionette, Ember, Angular

 — — modules/
 — — — — -MyModule/
 — — — — — — — — js/
 — — — — — — — — — -MyModule.js
 — — — — — — — — styles/

— — — — — — — — — -MyModule-layout.scss
 — — — — — — — — — -MyModule-theme.scss

— — — — — — — — templates/
 — — — — — — — — — -MyModule.hbs
 — — styles/
 — — — — -partials/
 — — — — — — — -_base.scss
 — — — — — — — -_buttons.scss
 — — — — — — — -_grid.scss

— — — — -global-styles.scss
 — — — — -_variables.scss

Naming Conventions

Encapsulate module styles using a unique selector prefix

Like BEM, Bandit has a naming convention. 
Only one strict rule: each selector in a module must have the same unique prefix. It could be the filename (if unique), it can be a composition. As long as it is unique. The rest is up to you.

Why the unique prefix? Encapsulated styles.

Unlike OOCSS and SMACSS, let’s not abstract as much as possible, let’s isolate as much as possible.

The styles for your module are confined, they won’t affect other parts of the application, they are kind of specificity risk free, so hopefully you will deploy with a free spirit ;)
You are also quite free to invent the naming convention of each module, everything after the first hyphen is scoped to that module. 
Or better, you can choose all together a set of conventions that naturally fits in your project.

Principles of Bandit

Principle — Flat hierarchy of class based selectors

From BEM.

The module’s unique identifier isolates the rules so there is no need to use regularly descendant selectors to control your styles.

The benefits are quite nice. The descendant selector is the most expensive selector in CSS so the goal is to avoid it when possible.

We will use descendant selectors for example when we need to override a rule of a module because of a state change:

Principle — Abstract and organize some basic styles

This comes from SMACSS. I think there should be a common set of classes for basic elements or components, like Resets/Normalize styles, buttons, typography rules, or very basic components like avatars or dropdowns. 
You could use a framework like Bootstrap or your own set of common styles.
Because of the first principle, we isolate the code, that means more code duplication*, so we want to have some basic styles abstracted:


Principle — Separate skin and structure

From OOCSS. Each module has two optional css files, one for the structural styles and one for skin, like the visual features. 
I call them -layout and -theme files:


CSS output:


*This means duplicated code!

The output of the previous two files, compressed, is 891 bytes. That is the size of the styles you needed for that module. If your project is composed of 100 modules we can still produce less than 100kb of CSS. 
If your code allows the injection of the module’s styles it’s even better. The code is loaded asynchronously together with the HTML it belongs to.

Rules of Bandit

Rule — Use variables for everything

Rule — No key selectors outside the module they belong to

Module key selectors should never be used outside the module files.

If you need to overrides styles because of a change in a parent that you need to consider in your module you can add a -overrides file in your module’s style folder:

Rule — Don’t nest selectors when it’s not necessary

The majority of your module selectors should have low specificity: 0 0 1 0.

Rule — Avoid #ID selectors

The specificity of an id selector is too high, it forces best avoided behaviours such as the !important declarations or inline styles to be overridden.

Rule — Avoid type selectors

Two big disadvantages:

  • The HTML structure is tightly coupled to the styles
  • Poor performance: selectors are evaluated right to left
From SMACSS: use class names as the right-most selector

Best practices of Bandit

Avoid extending selectors

It saves little but it can add unnecessary complexity to your files. The developer has to jump around files to find the mixin definition or worse, he/she is tempted to add arguments to it, potentially breaking the old behaviour. Let your module’s CSS files be expressive: the future you or a new developer will hate you less when code changes are needed in that selector.

Be responsive

Unlike other methodologies, avoid class names that express sizes in your markup. They can complicate your life when you are working with breakpoints.

Use Grids

Use bootstrap grid mixins, do your own, but use grids.
Have mixins to manage the structural rules, mixins to create grid elements such rows and columns for example.

Don’t abuse mixins

Have some, not many. 
Have mixins for the grid or have a mixin to add rules for truncating strings with ellipsis.

Think Mobile First

Even if you don’t need to. It address the problem of delivering unnecessary content.

Use tools for the grunt work

Let autoprefixer add the vendor specific styles.
Let a postcss plugin convert your inline assets to encoded strings.
Always use a linter like stylelint, i.e. prevent developers writing selectors with high specificity. There are many rules you can use to keep your code clean and lots of useful postcss plugins.

Review the code

As Zardoz Cys, wise colleague of mine, suggested to me:
Whether this be in the form of pair programming or a commit level code review tool with comments, multiple eyes help to keep the code clean.

Adopting a method is just the first step, the next one is for the advocates of the method to support the other developers.

Bending the rules of Bandit

Bandit is more what you’d call “guidelines” than actual rules
- Captain Hector Barbossa

Don’t sweat it

Selectors performance is a game to win 50ms, top. 

  • Don’t mess files up just because you can.
  • Try to forget that !important exists.
  • Write code that the next developer can understand.
  • Solve your problems with dedication.