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CSS + Sass # Principles of writing consistent, idiomatic CSS
==========
All of the following standards and practices on this page describe both CSS and Sass, unless otherwise noted. 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
Structure 1. [General principles](#general-principles)
--------- 2. [Whitespace](#whitespace)
3. [Comments](#comments)
4. [Format](#format)
5. [Practical example](#example)
- Use 4-space indents, not tabs [Acknowledgements](#acknowledgements)
- Add four blank lines between sections and one blank line between blocks in a section
- Each selector should be on its own line, ending in either a comma or an opening curly brace
- Property-value pairs can be on a single line, if there is only one pair for the selector, otherwise they should be on their own line
- Optionally, sets of property-value pairs can align vertically on the `:` chracter
- The closing brace should be left-aligned, using the same level of indentation as the opening selector
[License](#license)
#### Wrong
- Multiple selectors are on the same line <a name="general-principles"></a>
- The closing brace isn't left-aligned with the opening selector ## 1. General principles
- `.selector-4` has 2 property-value pairs on a single line. Only a single pair is allowed for shorthand single-line declarations.
``` > "Part of being a good steward to a successful project is realizing that
.selector-1, .selector-2, .selector-3 { > writing code for yourself is a Bad Idea™. If thousands of people are using
background: #fff; > your code, then write your code for maximum clarity, not your personal
color: #000; > preference of how to get clever within the spec." - Idan Gazit
}
.selector-4 { background: #f00; color: #000; } * 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.
<a name="whitespace"></a>
## 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.
<a name="comments"></a>
## 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
========================================================================== */
#### Good /* Sub-section comment block
========================================================================== */
- There are multiple property-value pairs, so aligning the colon characters could help readability. /**
* 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 */
``` ```
<a name="format"></a>
## 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-1,
.selector-2, .selector-2,
.selector-3 { .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: #fff;
color: #000; background: linear-gradient(#fff, rgba(0, 0, 0, 0.8));
}
.selector-a,
.selector-b {
padding: 10px;
} }
``` ```
#### Best #### 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;
}
``` ```
.selector-1,
.selector-2, Larger teams may prefer the simplicity and ease-of-maintenance that comes with
.selector-3 { alphabetical ordering.
background : #fff;
color : #000; #### 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;
} }
``` ```
\ No newline at end of file
### 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
}
```
<a name="example"></a>
## 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:
*
* <div class="grid">
* <div class="cell cell-3"></div>
* <div class="cell cell-3"></div>
* <div class="cell cell-3"></div>
* </div>
*/
/**
* 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;
}
```
Based on a work at
[github.com/necolas/idiomatic-css](https://github.com/necolas/idiomatic-css).
\ No newline at end of file