Our conventions for css and scss is comprised of variations of BEM, OOCSS, SUIT and airbnb.
A “rule declaration” is the name given to a selector (or a group of selectors) with an accompanying group of properties. Here’s an example:
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.listing {
font-size: 18px;
line-height: 1.2;
}
In a rule declaration, “selectors” are the bits that determine which elements in the DOM tree will be styled by the defined properties. Selectors can match HTML elements, as well as an element’s class, ID, or any of its attributes. Here are some examples of selectors:
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.my-element-class {
/* ... */
}
[aria-hidden] {
/* ... */
}
Finally, properties are what give the selected elements of a rule declaration their style. Properties are key-value pairs, and a rule declaration can contain one or more property declarations. Property declarations look like this:
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/* some selector */ {
background: #f1f1f1;
color: #333;
}
{ in rule declarations.: character.} of rule declarations on a new line.Bad
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.avatar{
border-radius:50%;
border:2px solid white; }
.no, .nope, .not_good {
// ...
}
#lol-no {
// ...
}
Good
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.avatar {
border-radius: 50%;
border: 2px solid white;
}
.one,
.selector,
.per-line {
// ...
}
// in Sass-land) to block comments.We encourage some combination of OOCSS and BEM for these reasons:
OOCSS, or “Object Oriented CSS”, is an approach for writing CSS that encourages you to think about your stylesheets as a collection of “objects”: reusable, repeatable snippets that can be used independently throughout a website.
BEM, or “Block-Element-Modifier”, is a naming convention for classes in HTML and CSS. It was originally developed by Yandex with large codebases and scalability in mind, and can serve as a solid set of guidelines for implementing OOCSS.
SUIT, or “Style tools for UI”, relies on structured class names and meaningful hyphens (i.e., not using hyphens merely to separate words). This helps to work around the current limits of applying CSS to the DOM (i.e., the lack of style encapsulation), and to better communicate the relationships between classes.
We recommend a variant of BEM with PascalCased “blocks”, which works particularly well when combined with components (e.g. React). Underscores and dashes are still used for modifiers and children.
Syntax: [<namespace>-]<ComponentName>[-descendentName][--modifierName]
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/* Utility */
.u-utilityName {}
/* Component */
.ComponentName {}
/* Component modifier */
.ComponentName--modifierName {}
/* Component descendant */
.ComponentName-descendant {}
/* Component descendant modifier */
.ComponentName-descendant--modifierName {}
/* Component state (scoped to component) */
.ComponentName.is-stateOfComponent {}
Example
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// ListingCard.jsx
function ListingCard() {
return (
<article class="ListingCard ListingCard--featured">
<h1 class="ListingCard-title">Adorable 2BR in the sunny Mission</h1>
<div class="ListingCard-content">
<p>Vestibulum id ligula porta felis euismod semper.</p>
</div>
</article>
);
}
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/* ListingCard.css */
.ListingCard { }
.ListingCard--featured { }
.ListingCard-title { }
.ListingCard-content { }
.ListingCard is the “block” and represents the higher-level component.ListingCard--title is an “element” and represents a descendant of .ListingCard that helps compose the block as a whole..ListingCard-featured is a “modifier” and represents a different state or variation on the .ListingCard block.While it is possible to select elements by ID in CSS, it should generally be considered an anti-pattern. ID selectors introduce an unnecessarily high level of specificity to your rule declarations, and they are not reusable.
For more on this subject, read CSS Wizardry’s article on dealing with specificity.
Avoid binding to the same class in both your CSS and JavaScript. Conflating the two often leads to, at a minimum, time wasted during refactoring when a developer must cross-reference each class they are changing, and at its worst, developers being afraid to make changes for fear of breaking functionality.
We recommend creating JavaScript-specific classes to bind to, prefixed with .js-:
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<button class="btn btn-primary js-request-to-book">Request to Book</button>
Use 0 instead of none to specify that a style has no border.
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.foo {
border: none;
}
Good
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.foo {
border: 0;
}
.scss syntax, never the original .sass syntax@include declarations logically (see below)Property declarations
List all standard property declarations, anything that isn’t an @include or a nested selector.
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.btn-green {
background: green;
font-weight: bold;
// ...
}
@include declarations
Grouping @includes at the end makes it easier to read the entire selector.
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.btn-green {
background: green;
font-weight: bold;
@include transition(background 0.5s ease);
// ...
}
Nested selectors
Nested selectors, if necessary, go last, and nothing goes after them. Add whitespace between your rule declarations and nested selectors, as well as between adjacent nested selectors. Apply the same guidelines as above to your nested selectors.
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.btn {
background: green;
font-weight: bold;
@include transition(background 0.5s ease);
.icon {
margin-right: 10px;
}
}
Prefer dash-cased variable names (e.g. $my-variable) over camelCased or snake_cased variable names. It is acceptable to prefix variable names that are intended to be used only within the same file with an underscore (e.g. $--my-variable).
Mixins should be used to DRY up your code, add clarity, or abstract complexity–in much the same way as well-named functions. Mixins that accept no arguments can be useful for this, but note that if you are not compressing your payload (e.g. gzip), this may contribute to unnecessary code duplication in the resulting styles.
@extend should be avoided because it has unintuitive and potentially dangerous behavior, especially when used with nested selectors. Even extending top-level placeholder selectors can cause problems if the order of selectors ends up changing later (e.g. if they are in other files and the order the files are loaded shifts). Gzipping should handle most of the savings you would have gained by using @extend, and you can DRY up your stylesheets nicely with mixins.
Do not nest selectors more than three levels deep!
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.page-container {
.content {
.profile {
// STOP!
}
}
}
When selectors become this long, you’re likely writing CSS that is:
Again: never nest ID selectors!
If you must use an ID selector in the first place (and you should really try not to), they should never be nested. If you find yourself doing this, you need to revisit your markup, or figure out why such strong specificity is needed. If you are writing well formed HTML and CSS, you should never need to do this.
Under no circumstance should you use !important it is only permitted in overrides, however inheritance will work better.
Most of our projects use bootstrap as a our starting point. When you need to change something, try to change the source first. This means going into the un minified version of bootstrap and changing the styles you want.