CSS

Directory structure

├── podspec.yaml
├── source/
|   ├── sass/
|   |   ├── mixins/
|   |   |   ├── _breakpoints.sass
|   |   |   ├── _type.sass
|   |   |   ├── ...
|   |   ├── macros/
|   |   |   ├── _<macro>.sass
|   |   |   ├── ...
|   |   ├── partials/
|   |   |   ├── _<partial>.sass
|   |   |   ├── ...
|   |   ├── vendor/
|   |   |   ├── ...
|   |   ├── _base.sass
|   |   ├── _vars.sass
|   |   ├── ...
|   |   └── main.sass

Naming conventions

  • Use URL-style casing (lowercase, hyphen-delimited) for files, variables, functions, animations, mixins, etc.
  • Avoid using underscores or camel case to separate words.
  • Avoid prefixing with your project name, unless your website is specifically required to embed within a dirty CSS space.

Use BEM

  • Use BEM, and follow it strictly.
  • Avoid styling IDs.
  • Avoid styling HTML elements (use div over semantic elements).*

*This may negatively impact accessibility. To build an accessible site with this approach, make sure to use the proper aria and role attributes on elements.

Class names should follow content structure

  • BEM names should correspond directly to the partial and its structure.
  • File names should be consistent with the view (the partial and/or the macro).
  • There should be one CSS (Sass) file per partial template.
/content/partials/foo.yaml
partial: foo
title: My title.
body: My body.
/views/partials/foo.html
<div class="foo {{partial.class}}">
  <div class="foo__title">{{partial.title}}</div>
  <div class="foo__body">{{partial.body}}</div>
</div>
/source/sass/partials/_foo.sass
.foo
  background: grey

.foo__title
  font-weight: bold

.foo__body
  color: red

Syntax

Keep it flat

Avoid using nesting and the Sass ampersand (&) to create BEM structures. This creates legibility and maintainability issues. A flat structure will be easier to audit and quickly understand, and avoids indendation mistakes.

.gallery
  ...
.gallery__title
  ...
.gallery__item
  ...
  &--active
    ...
.gallery__item__description
  ...
  &--active
    ...
.gallery__item__footer
  ...
  @at-root [dir=rtl] &
    ...
.gallery__item__author
  ...
Do
.gallery
    ...
  &__title
    ...
  &__item
      ...
    &--active
      ...
    &__description
      ...
        &--active
          ...
    &__footer
      ...
      @at-root [dir=rtl] &
        ...
    &__author
      ...
Don't

Use mixins over extends

Use Sass mixins (+) over Sass extends (%), including mixins without arguments. Style sheets created with extends create unnecessary coupling and can introduce mistakes. Style sheets created with mixins are further encapsulated. Choosing one also removes the need to make a decision when creating new rules.

Partial variations

Style variations of a partial intended to be used with {{partial.class}} should be encapsulated and placed at the end of the Sass file, rather that sprinkling variations throughout the file. This keeps all code related to one variation in one place, and keeps the rest of the file clean.

All changes created by a variation can be quickly understood, and the variation can be easily deleted later if it is no longer needed.

.gallery
  ...

.gallery--large
  .gallery__title
    font-size: 1.5em

  .gallery__footer
    font-size: 1.25em

  .gallery__image
    transform: scale(1.5)
Do
.gallery
  ...

.gallery__title
  @at-root .gallery--large &
    font-size: 1.5em

.gallery__footer
  @at-root .gallery--large &
    font-size: 1.25em

.gallery__image
  @at-root .gallery--large &
    transform: scale(1.5)
Don't

Element usage

  • Use div elements for all layout, with proper aria and role attributes for accessibility.
  • Avoid using semantic HTML elements in site structure.
  • Use semantic HTML and styles only for elements within user-supplied (or content manager-supplied) content (such as Markdown or "textarea fields" from a CMS).
  • Don't use reset stylesheets.

Using div removes the need to guess which HTML element should correctly satisfy a design. It also removes the need for a reset stylesheet, and permits default styles for semantic elements to be (correctly) applied to large Markdown blocks or user-supplied content.

Repeated rules and sizes

  • Create mixins and variables for repeated rules and sizes.
  • Avoid hard-coding sizes and reused values.