eResults CSS/SCSS Styleguide

A mostly reasonable approach to CSS and Sass

Table of Contents

1. Terminology
   • Rule Declaration
   • Selectors
   • Properties
2. CSS
   • Formatting
   • Property order
   • Comments
   • OOCSS and BEM
   • ID Selectors
   • JavaScript hooks
   • Border
3. Sass
   • Syntax
   • Ordering
   • Variables
   • Mixins
   • Extend directive
   • Nested selectors
4. Directory structure

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 (4 spaces) for indentation
• Use BEM style class names and formatting rules (- to separate words, __ for modules and -- for modifiers)
• Do not use ID selectors
• Prefer combined properties whenever possible (eg. combine font-family, font-size, font-weight etc. in font)
• 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
• End every file with a blank line

Bad

.avatar{
    border-radius:50%;
    border:2px solid white;
    font-family: Arial;
    font-size: 12px;
    font-weight: bold;}
.no, .nope, .not_good {
    // ...
}
#lol-no {
  // ...
}

Good

.avatar {
  border-radius: 50%;
  border: 2px solid white;
  font: bold 12px Arial;
}

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

Property order

Use the Layout Box Visual Type grouping to sort your properties. See https://pyx.space/post/keys-to-maintainable-css-order for more information.

Bad

.avatar {
    background: blue;
    border:2px solid white;
    display: block;
    font-size: 12px;
    position: absolute;
}

Good

.avatar {
    position: absolute;
    
    display: block;
    
    background: blue;
    border:2px solid white;
    
    font-size: 12px;
}

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

BEM

We require 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

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

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 */
.listing-card { }
.listing-card--featured { }
.listing-card__title { }
.listing-card__content { }

• .listing-card is the “block” and represents the higher-level component
• .listing-card__title is an “element” and represents a descendant of .ListingCard that helps compose the block as a whole.
• .listing-card--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.

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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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 in alphabetical order, anything that isn't an @include or a nested selector. When useful create separate property groups, for example when defining position.

   .button-green {
     background: green;
     font-weight: bold;
     
     position: absolute;
     bottom: 0;
     left: 0;
     right: 0;
     top: 0;
   }

2. @include declarations

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

   .button-green {
     background: green;
     font-weight: bold;
     @include position(absolute, 0, 0, 0, 0);
     // ...
   }

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 and the component name (e.g. $_my-component__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

Do not use @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 {
  .page-container__content {
    .page-container__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.

Directory structure

When using BEM the default directory structure will usually be similar to:

• base Contains styling files for the base layer of the website for parts that don't fall under a specific component, like typography and style defaults/resets
• components A seperate file for each component
• design Various files that define variables about the design, like colors, typography and margins/paddings
• mixins Define your mixins, one per file
• main.scss Entry file which includes all other files, doesn't contain any style rules itself

Each directory should have a single index.scss file, which includes all other files in the directory. Allowing the entire folder to be easily included.

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