A mostly reasonable approach to CSS and Sass
When you don't know if you can use a certain way of styling, see https://caniuse.com to check. Sass language reference: https://sass-lang.com/. What are CSS Modules: CSS Modules documentation.
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;
}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] {
/* ... */
}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;
}- Use soft tabs (2 spaces) for indentation.
- Use camelCase in class names (see CSS Modules).
- Use dashes outside of CSS modules
- 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 {
// ...
}- 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
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.
- Use the
.scsssyntax, never the original.sasssyntax - Order your regular CSS and
@includedeclarations logically (see below)
-
Property declarations
List all standard property declarations, anything that isn't an
@includeor a nested selector..btn-green { background: green; font-weight: bold; // ... }
-
@includedeclarationsGrouping
@includes at the beginning makes it easier to read the entire selector and allows to override parts of the mixin..btn-green { @include transition(background 0.5s ease); // ... background: green; font-weight: bold; }
-
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 { @include transition(background 0.5s ease); background: green; font-weight: bold; .icon { margin-right: 10px; } }
Prefer dash-cased or camelCased variable names (e.g. $my-variable) over 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 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 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.
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.
We prefer using mixins over functions. If a function is absolutely necessary, document where it is used and why it wasn't possible to create a mixin.
- Prefer using CSS Modules over global css code
- Always use
.module.cssor.module.scssextension - Use camelCase for class names
// bad
.foo-bar {
color: red;
}
// good
.fooBar {
color: red;
}import styles from "./foo.module.scss"
// ...
// bad
return <div className={styles['foo-bar']}>
// good
return <div className={styles.fooBar}>- Use simple class and variable names since both are scoped to the module
- Do not expect any scss variables or mixins to be defined. You have to import them yourself.
- Use Sass whenever possible over similar CSS module functionality (composition, variables, import)
- CSS or Sass specific rules still apply (CSS Modules rules take precedence)
- inline class names, only extract if they get very very long or when they are used multiple times
import styles from "./foo.module.scss"
// ...
// bad
const someClassName = styles.fooBar;
return <div className={someClassName}>
// good
return <div className={styles.fooBar}>