gitlab-org--gitlab-foss/doc/development/fe_guide/style_guide_scss.md

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# SCSS styleguide
This style guide recommends best practices for SCSS to make styles easy to read,
easy to maintain, and performant for the end-user.
## Rules
### Naming
CSS classes should use the `lowercase-hyphenated` format rather than
`snake_case` or `camelCase`.
```scss
// Bad
.class_name {
color: #fff;
}
// Bad
.className {
color: #fff;
}
// Good
.class-name {
color: #fff;
}
```
### Formatting
You should always use a space before a brace, braces should be on the same
line, each property should each get its own line, and there should be a space
between the property and its value.
```scss
// Bad
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.container-item {
width: 100px; height: 100px;
margin-top: 0;
}
// Bad
.container-item
{
width: 100px;
height: 100px;
margin-top: 0;
}
// Bad
.container-item{
width:100px;
height:100px;
margin-top:0;
}
// Good
.container-item {
width: 100px;
height: 100px;
margin-top: 0;
}
```
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Note that there is an exception for single-line rulesets, although these are
not typically recommended.
```scss
p { margin: 0; padding: 0; }
```
### Colors
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HEX (hexadecimal) colors should use shorthand where possible, and should use
lower case letters to differentiate between letters and numbers, e.g. `#E3E3E3`
vs. `#e3e3e3`.
```scss
// Bad
p {
color: #ffffff;
}
// Bad
p {
color: #FFFFFF;
}
// Good
p {
color: #fff;
}
```
### Indentation
Indentation should always use two spaces for each indentation level.
```scss
// Bad, four spaces
p {
color: #f00;
}
// Good
p {
color: #f00;
}
```
### Semicolons
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Always include semicolons after every property. When the stylesheets are
minified, the semicolons will be removed automatically.
```scss
// Bad
.container-item {
width: 100px;
height: 100px
}
// Good
.container-item {
width: 100px;
height: 100px;
}
```
### Shorthand
The shorthand form should be used for properties that support it.
```scss
// Bad
margin: 10px 15px 10px 15px;
padding: 10px 10px 10px 10px;
// Good
margin: 10px 15px;
padding: 10px;
```
### Zero Units
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Omit length units on zero values, they're unnecessary and not including them
is slightly more performant.
```scss
// Bad
.item-with-padding {
padding: 0px;
}
// Good
.item-with-padding {
padding: 0;
}
```
### Selectors with a `js-` Prefix
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Do not use any selector prefixed with `js-` for styling purposes. These
selectors are intended for use only with JavaScript to allow for removal or
renaming without breaking styling.
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### IDs
Don't use ID selectors in CSS.
```scss
// Bad
#my-element {
padding: 0;
}
// Good
.my-element {
padding: 0;
}
```
### Variables
Before adding a new variable for a color or a size, guarantee:
1. There isn't already one
2. There isn't a similar one we can use instead.
## Linting
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We use [SCSS Lint][scss-lint] to check for style guide conformity. It uses the
ruleset in `.scss-lint.yml`, which is located in the home directory of the
project.
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To check if any warnings will be produced by your changes, you can run `rake
scss_lint` in the GitLab directory. SCSS Lint will also run in GitLab CI to
catch any warnings.
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If the Rake task is throwing warnings you don't understand, SCSS Lint's
documentation includes [a full list of their linters][scss-lint-documentation].
### Fixing issues
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If you want to automate changing a large portion of the codebase to conform to
the SCSS style guide, you can use [CSSComb][csscomb]. First install
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[Node][node] and [NPM][npm], then run `npm install csscomb -g` to install
CSSComb globally (system-wide). Run it in the GitLab directory with
`csscomb app/assets/stylesheets` to automatically fix issues with CSS/SCSS.
Note that this won't fix every problem, but it should fix a majority.
### Ignoring issues
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If you want a line or set of lines to be ignored by the linter, you can use
`// scss-lint:disable RuleName` ([more info][disabling-linters]):
```scss
// This lint rule is disabled because the class name comes from a gem.
// scss-lint:disable SelectorFormat
.ui_charcoal {
background-color: #333;
}
// scss-lint:enable SelectorFormat
```
Make sure a comment is added on the line above the `disable` rule, otherwise the
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linter will throw a warning. `DisableLinterReason` is enabled to make sure the
style guide isn't being ignored, and to communicate to others why the style
guide is ignored in this instance.
[csscomb]: https://github.com/csscomb/csscomb.js
[node]: https://github.com/nodejs/node
[npm]: https://www.npmjs.com/
[scss-lint]: https://github.com/brigade/scss-lint
[scss-lint-documentation]: https://github.com/brigade/scss-lint/blob/master/lib/scss_lint/linter/README.md
[disabling-linters]: https://github.com/brigade/scss-lint#disabling-linters-via-source