CSS

A guide for writting sane css.

Flavor

We use SCSS instead of plain CSS. It allows for really neat, organised CSS.

Formatting

  • Use soft tabs (2 spaces) for indentation
  • Prefer dashes over camelCasing in class names.
    • Underscores and PascalCasing are okay if you are using BEM (see OOCSS and BEM below).
  • 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
  • Use the .scss syntax, never the original .sass syntax
  • Order your regular CSS and @include declarations logically (see below)
  • Use Auto-prefixer.
  • Prefer to use Bourbon for Sass Mixings.
  • Prefer using Neat for symantic grid and breakpoint declorations.

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.

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.

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.

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- or 'data-' attributes.:

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

Ordering of property declarations

  1. Property declarations

    List all standard property declarations, anything that isn't an @include or a nested selector.

     .btn-green {
       background: green;
       font-weight: bold;
       // ...
     }
    
  2. @include declarations

    Grouping @includes at the end makes it easier to read the entire selector.

     .btn-green {
       background: green;
       font-weight: bold;
       @include transition(background 0.5s ease);
       // ...
     }
    
  3. 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.

     .btn {
       background: green;
       font-weight: bold;
       @include transition(background 0.5s ease);
    
       .icon {
         margin-right: 10px;
       }
     }
    

Variables

Prefer dash-cased variable names (e.g. $my-variable) over camelCased or snake_cased variable names.

Mixins

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 directive

@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.

Nested selectors

Do not nest selectors more than three levels deep!

.page-container {
  .content {
    .profile {
      // STOP!
    }
  }
}

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