CSS Style Guide

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 :

<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>

/* file.css */
.ListingCard { }
.ListingCard--featured { }
.ListingCard__title { }
.ListingCard__content { }

/* file.scss */
.ListingCard { 
    &--featured { }
    &__title { }
    &__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.

Sass

Syntax

• Use the .scss syntax, never the original .sass syntax

• Order your regular CSS and @include declarations logically (see below)

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. 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

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!
    }
  }
}

When selectors become this long, you're likely writing CSS that is:

• Strongly coupled to the HTML (fragile) —OR—

• Overly specific (powerful) —OR—

• Not reusable

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.

Background and content url best practice

Background url and content url writing. This is our way of dealing with changing domains from local to staging to live websites

// Bad 
.background {
    background: url('https://staging.classict.nl/wp-content/uploads/2022/04/partner-image-2.png');
}

// Good
.background {
    background: url('/wp-content/uploads/2022/04/partner-image-2.png');
}

Reference:

• https://github.com/airbnb/css