css

Cisco Spark CSS Styleguide

A mostly reasonable approach to CSS adapted from the Airbnb CSS styleguide

Table of Contents

1. Terminology
   • Rule Declaration
   • Selectors
   • Properties
2. CSS
   • Formatting
   • Comments
   • OOCSS and BEM
   • ID Selectors
   • JavaScript hooks
   • Border
3. CSS modules
   • Syntax
   • Variables
   • Mixins

Terminology

Rule declaration

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:

.listing {
  font-size: 18px;
  line-height: 1.2;
}

Selectors

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:

.my-element-class {
  /* ... */
}

[aria-hidden] {
  /* ... */
}

Properties

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:

/* some selector */ {
  background: #f1f1f1;
  color: #333;
}

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CSS

Formatting

• Use soft tabs (2 spaces) for indentation
• Prefer dashes over camelCasing in class names.
• Do not use ID selectors
• When using multiple selectors in a rule declaration, give each selector its own line.
• Put a space before the opening brace { in rule declarations
• In properties, put a space after, but not before, the : character.
• Put closing braces } of rule declarations on a new line
• Put blank lines between rule declarations

Bad

.avatar{
    border-radius:50%;
    border:2px solid white; }
.no, .nope, .not_good {
    // ...
}
#lol-no {
  // ...
}

Good

.avatar {
  border-radius: 50%;
  border: 2px solid white;
}

.one,
.selector,
.per-line {
  // ...
}

Comments

• Prefer line comments (// in Sass-land) to block comments.
• Prefer comments on their own line. Avoid end-of-line comments.
• Write detailed comments for code that isn't self-documenting:
  • Uses of z-index
  • Compatibility or browser-specific hacks

OOCSS and BEM

We encourage some combination of OOCSS and BEM for these reasons:

• It helps create clear, strict relationships between CSS and HTML
• It helps us create reusable, composable components
• It allows for less nesting and lower specificity
• It helps in building scalable stylesheets

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.

• Nicole Sullivan's OOCSS wiki
• Smashing Magazine's Introduction to OOCSS

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.

• CSS Trick's BEM 101
• Harry Roberts' introduction to BEM

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.

Example

// 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>
  );
}

/* 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.

ID selectors

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.

JavaScript hooks

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-:

<button class="btn btn-primary js-request-to-book">Request to Book</button>

Border

Use 0 instead of none to specify that a style has no border.

Bad

.foo {
  border: none;
}

Good

.foo {
  border: 0;
}

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CSS Modules

CSS modules is a great way to conflict free, local scoping for the styles that you write. We generally use it for projects that have a built in compile step. You can read more about it here https://github.com/css-modules/css-modules