An intro to CSS Methodologies

This is based off of a presentation I put together for an intro to CSS Methodologies. I thought it might be beneficial to write it out here (as opposed to only having it in Powerpoint). I apologize if some of the descriptions are brief, as it was written to be accompanied by my speaking :)

Object Oriented CSS (OOCSS)

Objects in front-end development are simply HTML elements. The CSS is where we make those objects, or elements, modular and location independent to be able to place them anywhere on a page and behave predictably.

Basic principles:

Separating structure from skin:

To abstract the structure and positioning styles of an object from the presentational styles, or skin.

Separating container from content:

To break components’ dependency of their containers. Any object should be able to be placed in another container and still look and behave the same.


Separating Structure

In other words: Position, float, margin, etc from background-color, border, etc

Essentially, don’t mix structure/positioning properties with skin/styling properties on the same class.

Skinning properties and be reused on a variety of elements, preventing property duplication.

Separating Container

Allow re-use of elements no mater where you are in the dom. Styled element should never be dependent on where it’s at in a page.

“Rarely use location-dependent styles.” Do not cascade, go straight into object, give them a class and reference that in your CSS.

Don’t do this:

ul li.list-item {

Instead, go straight into the element:

.list-item {

Never mimic the structure of your HTML in CSS. In other words, don’t refer to tags or IDs in your stylesheets. Instead, try to create and apply a classes that describe the use of the tag in question. And keep nested classes to a bare minimum.

The “Media” Object

Poster child for OOCSS, the “media” object is an image to the left, with descriptive content to the right. The content on the right can contain any other objects, text, lists, other media objects

Properties of the media object:

.media {margin:10px;}
.media, .bd {overflow:hidden; _overflow:visible; zoom:1;}
.media .img {float:left; margin-right: 10px;}
.media .img img {display:block;}
.media .imgExt {float:right; margin-left: 10px;}



Using Sass @extend with placeholder classes cleans up your HTML leaving you with semantic class names while still remaining DRY.

Placeholder classes reduce the bloat of extending real classes or using mixing, and if you decide later that you don’t want an element to have that certain style pattern, all you have to do is remove the @extend line instead of going through the HTML and taking it out everywhere.

Placeholders also can be re-used among projects

// Using the media element example (Facebook)

%media {
     overflow: hidden;
     &:first-child {
          float: left;
     &:last-child {
         overflow: hidden;

.status {
     @extend %media;
     // Status specific styles

.profile {
     @extend %media;
     // Profile specific styles

With BEM

Stands for Block Element Modifier, and it’s sort of a way to write OOCSS.

Each block starts with a block (object name). Children of that block are elements, separated by two underscores. Modifiers are added by two hyphens.

.block {}
.block__element {}
.block--modifier {}
// Media object in BEM

.media {}
.media__img {}
.media__img--rev {}
.media__body {}

It really aims to not have an descendant selectors.

You can still use it with Sass though, by using the & to prefix the elements

.media {
     &__img { }

What about Smacss?

“Scalable and modular architecture for CSS” A style guide for your CSS - Widely considered a “must read” Check out the book here- $15.00

Categorization is at the very core of SMACSS.

The purpose of categorization is to find patterns. It’s hard at first to decide what pieces go into what category, but that is all part of the process - it forces you to think.


Naming conventions help to automatically distinguish which category a rule belongs to.



MindBEMding – getting your head ’round BEM syntax



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