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https://github.com/necolas/idiomatic-css

Principles of writing consistent, idiomatic CSS.
https://github.com/necolas/idiomatic-css

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Principles of writing consistent, idiomatic CSS.

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# Principles of writing consistent, idiomatic CSS



The following document outlines a reasonable style guide for CSS development.

These guidelines strongly encourage the use of existing, common, sensible

patterns. They should be adapted as needed to create your own style guide.



This is a living document and new ideas are always welcome. Please

contribute.



## Table of contents



1. [General principles](#general-principles)

2. [Whitespace](#whitespace)

3. [Comments](#comments)

4. [Format](#format)

5. [Practical example](#example)



[Acknowledgements](#acknowledgements)



[License](#license)





## 1. General principles



> "Part of being a good steward to a successful project is realizing that

> writing code for yourself is a Bad Idea™. If thousands of people are using

> your code, then write your code for maximum clarity, not your personal

> preference of how to get clever within the spec." - Idan Gazit



* Don't try to prematurely optimize your code; keep it readable and

  understandable.

* All code in any code-base should look like a single person typed it, even

  when many people are contributing to it.

* Strictly enforce the agreed-upon style.

* If in doubt when deciding upon a style use existing, common patterns.





## 2. Whitespace



Only one style should exist across the entire source of your code-base. Always

be consistent in your use of whitespace. Use whitespace to improve

readability.



* _Never_ mix spaces and tabs for indentation.

* Choose between soft indents (spaces) or real tabs. Stick to your choice

  without fail. (Preference: spaces)

* If using spaces, choose the number of characters used per indentation level.

  (Preference: 4 spaces)



Tip: configure your editor to "show invisibles" or to automatically remove

end-of-line whitespace.



Tip: use an [EditorConfig](http://editorconfig.org/) file (or equivalent) to

help maintain the basic whitespace conventions that have been agreed for your

code-base.





## 3. Comments



Well commented code is extremely important. Take time to describe components,

how they work, their limitations, and the way they are constructed. Don't leave

others in the team guessing as to the purpose of uncommon or non-obvious

code.



Comment style should be simple and consistent within a single code base.



* Place comments on a new line above their subject.

* Keep line-length to a sensible maximum, e.g., 80 columns.

* Make liberal use of comments to break CSS code into discrete sections.

* Use "sentence case" comments and consistent text indentation.



Tip: configure your editor to provide you with shortcuts to output agreed-upon

comment patterns.



Example:



```css

/* ==========================================================================

   Section comment block

   ========================================================================== */



/* Sub-section comment block

   ========================================================================== */



/**

 * Short description using Doxygen-style comment format

 *

 * The first sentence of the long description starts here and continues on this

 * line for a while finally concluding here at the end of this paragraph.

 *

 * The long description is ideal for more detailed explanations and

 * documentation. It can include example HTML, URLs, or any other information

 * that is deemed necessary or useful.

 *

 * @tag This is a tag named 'tag'

 *

 * TODO: This is a todo statement that describes an atomic task to be completed

 *   at a later date. It wraps after 80 characters and following lines are

 *   indented by 2 spaces.

 */



/* Basic comment */

```





## 4. Format



The chosen code format must ensure that code is: easy to read; easy to clearly

comment; minimizes the chance of accidentally introducing errors; and results

in useful diffs and blames.



* Use one discrete selector per line in multi-selector rulesets.

* Include a single space before the opening brace of a ruleset.

* Include one declaration per line in a declaration block.

* Use one level of indentation for each declaration.

* Include a single space after the colon of a declaration.

* Use lowercase and shorthand hex values, e.g., `#aaa`.

* Use single or double quotes consistently. Preference is for double quotes,

  e.g., `content: ""`.

* Quote attribute values in selectors, e.g., `input[type="checkbox"]`.

* _Where allowed_, avoid specifying units for zero-values, e.g., `margin: 0`.

* Include a space after each comma in comma-separated property or function

  values.

* Include a semi-colon at the end of the last declaration in a declaration

  block.

* Place the closing brace of a ruleset in the same column as the first

  character of the ruleset.

* Separate each ruleset by a blank line.



```css

.selector-1,

.selector-2,

.selector-3[type="text"] {

    -webkit-box-sizing: border-box;

    -moz-box-sizing: border-box;

    box-sizing: border-box;

    display: block;

    font-family: helvetica, arial, sans-serif;

    color: #333;

    background: #fff;

    background: linear-gradient(#fff, rgba(0, 0, 0, 0.8));

}



.selector-a,

.selector-b {

    padding: 10px;

}

```



#### Declaration order



If declarations are to be consistently ordered, it should be in accordance with

a single, simple principle.



Smaller teams may prefer to cluster related properties (e.g. positioning and

box-model) together.



```css

.selector {

    /* Positioning */

    position: absolute;

    z-index: 10;

    top: 0;

    right: 0;

    bottom: 0;

    left: 0;



    /* Display & Box Model */

    display: inline-block;

    overflow: hidden;

    box-sizing: border-box;

    width: 100px;

    height: 100px;

    padding: 10px;

    border: 10px solid #333;

    margin: 10px;



    /* Other */

    background: #000;

    color: #fff;

    font-family: sans-serif;

    font-size: 16px;

    text-align: right;

}

```



Larger teams may prefer the simplicity and ease-of-maintenance that comes with

alphabetical ordering.



#### Exceptions and slight deviations



Large blocks of single declarations can use a slightly different, single-line

format. In this case, a space should be included after the opening brace and

before the closing brace.



```css

.selector-1 { width: 10%; }

.selector-2 { width: 20%; }

.selector-3 { width: 30%; }

```



Long, comma-separated property values - such as collections of gradients or

shadows - can be arranged across multiple lines in an effort to improve

readability and produce more useful diffs. There are various formats that could

be used; one example is shown below.



```css

.selector {

    background-image:

        linear-gradient(#fff, #ccc),

        linear-gradient(#f3c, #4ec);

    box-shadow:

        1px 1px 1px #000,

        2px 2px 1px 1px #ccc inset;

}

```



### Preprocessors: additional format considerations



Different CSS preprocessors have different features, functionality, and syntax.

Your conventions should be extended to accommodate the particularities of any

preprocessor in use. The following guidelines are in reference to Sass.



* Limit nesting to 1 level deep. Reassess any nesting more than 2 levels deep.

  This prevents overly-specific CSS selectors.

* Avoid large numbers of nested rules. Break them up when readability starts to

  be affected. Preference to avoid nesting that spreads over more than 20

  lines.

* Always place `@extend` statements on the first lines of a declaration

  block.

* Where possible, group `@include` statements at the top of a declaration

  block, after any `@extend` statements.

* Consider prefixing custom functions with `x-` or another namespace. This

  helps to avoid any potential to confuse your function with a native CSS

  function, or to clash with functions from libraries.



```scss

.selector-1 {

    @extend .other-rule;

    @include clearfix();

    @include box-sizing(border-box);

    width: x-grid-unit(1);

    // other declarations

}

```





## 5. Practical example



An example of various conventions.



```css

/* ==========================================================================

   Grid layout

   ========================================================================== */



/**

 * Column layout with horizontal scroll.

 *

 * This creates a single row of full-height, non-wrapping columns that can

 * be browsed horizontally within their parent.

 *

 * Example HTML:

 *

 * 


 *     


 *     


 *     


 * 


 */



/**

 * Grid container

 *

 * Must only contain `.cell` children.

 *

 * 1. Remove inter-cell whitespace

 * 2. Prevent inline-block cells wrapping

 */



.grid {

    height: 100%;

    font-size: 0; /* 1 */

    white-space: nowrap; /* 2 */

}



/**

 * Grid cells

 *

 * No explicit width by default. Extend with `.cell-n` classes.

 *

 * 1. Set the inter-cell spacing

 * 2. Reset white-space inherited from `.grid`

 * 3. Reset font-size inherited from `.grid`

 */



.cell {

    position: relative;

    display: inline-block;

    overflow: hidden;

    box-sizing: border-box;

    height: 100%;

    padding: 0 10px; /* 1 */

    border: 2px solid #333;

    vertical-align: top;

    white-space: normal; /* 2 */

    font-size: 16px; /* 3 */

}



/* Cell states */



.cell.is-animating {

    background-color: #fffdec;

}



/* Cell dimensions

   ========================================================================== */



.cell-1 { width: 10%; }

.cell-2 { width: 20%; }

.cell-3 { width: 30%; }

.cell-4 { width: 40%; }

.cell-5 { width: 50%; }



/* Cell modifiers

   ========================================================================== */



.cell--detail,

.cell--important {

    border-width: 4px;

}

```



## Translations



* [Bahasa Indonesia](https://github.com/necolas/idiomatic-css/tree/master/translations/id-ID)

* [Bulgarian](https://github.com/vestimir/idiomatic-css)

* [Česky](https://github.com/necolas/idiomatic-css/tree/master/translations/cs-CZ)

* [Dansk](https://github.com/necolas/idiomatic-css/tree/master/translations/da-DK)

* [Deutsch](https://github.com/necolas/idiomatic-css/tree/master/translations/de-DE)

* [Español](https://github.com/necolas/idiomatic-css/tree/master/translations/es-ES)

* [Français](https://github.com/necolas/idiomatic-css/tree/master/translations/fr-FR)

* [Italiano](https://github.com/necolas/idiomatic-css/tree/master/translations/it-IT)

* [日本語](https://github.com/necolas/idiomatic-css/tree/master/translations/ja-JP)

* [한국어](https://github.com/necolas/idiomatic-css/tree/master/translations/ko-KR)

* [Nederlands](https://github.com/necolas/idiomatic-css/tree/master/translations/nl-NL)

* [Polski](https://github.com/necolas/idiomatic-css/tree/master/translations/pl-PL)

* [Português (Brasil)](https://github.com/necolas/idiomatic-css/tree/master/translations/pt-BR)

* [Русский](https://github.com/necolas/idiomatic-css/tree/master/translations/ru-RU)

* [Srpski](https://github.com/necolas/idiomatic-css/tree/master/translations/sr-SR)

* [Türkçe](https://github.com/necolas/idiomatic-css/tree/master/translations/tr-TR)

* [正體中文](https://github.com/necolas/idiomatic-css/tree/master/translations/zh-TW)

* [简体中文](https://github.com/necolas/idiomatic-css/tree/master/translations/zh-CN)





## Acknowledgements



Thanks to everyone who has provided translations and to all those who

contributed to [idiomatic.js](https://github.com/rwldrn/idiomatic.js). It was a

source of inspiration, quotations, and guidelines.





## License



_Principles of writing consistent, idiomatic CSS_ by Nicolas Gallagher is

licensed under the [Creative Commons Attribution 3.0 Unported

License](http://creativecommons.org/licenses/by/3.0/). This applies to all

documents and translations in this repository.



Based on a work at

[github.com/necolas/idiomatic-css](https://github.com/necolas/idiomatic-css).