> 参考：
http://alloyteam.github.io/CodeGuide/ (腾讯前端代码规范)
http://www.waylau.com/css-code-guide/
[TOC]
# 缩进
使用 soft tab（4个空格）。
~~~
.element {
position: absolute;
top: 10px;
left: 10px;
border-radius: 10px;
width: 50px;
height: 50px;
}
~~~
# 分号
每个属性声明末尾都要加分号。
~~~
.element {
width: 20px;
height: 20px;
background-color: red;
}
~~~
# 空格
* 以下几种情况不需要空格：
▫ 属性名后
▫ 多个规则的分隔符`,`前
▫ !important `!`后
▫ 属性值中`(`后和`)`前
▫ 行末不要有多余的空格
* 以下几种情况需要空格：
▫ 属性值前
▫ 选择器`>`, `+`,`` ~``前后
▫ `{`前
▫ !important `!`前
▫ `@else` 前后
▫ 属性值中的`,`后
▫ 注释``/*后和`*/`前
~~~
/* not good */
.element {
color :red! important;
background-color: rgba(0,0,0,.5);
}
/* good */
.element {
color: red !important;
background-color: rgba(0, 0, 0, .5);
}
/* not good */
.element ,
.dialog{
...
}
/* good */
.element,
.dialog {
}
/* not good */
.element>.dialog{
...
}
/* good */
.element > .dialog{
...
}
/* not good */
.element{
...
}
/* good */
.element {
...
}
/* not good */
@if{
...
}@else{
...
}
/* good */
@if {
...
} @else {
...
}
~~~
# 空行
* 以下几种情况需要空行：
▫ 文件最后保留一个空行
▫ `}`后最好跟一个空行，包括scss中嵌套的规则
▫ 属性之间需要适当的空行，具体见属性声明顺序
~~~
/* not good */
.element {
...
}
.dialog {
color: red;
&:after {
...
}
}
/* good */
.element {
...
}
.dialog {
color: red;
&:after {
...
}
}
~~~
# 换行
* 以下几种情况不需要换行：
▫ {`前
* 以下几种情况需要换行：
▫ `{`后和`}`前
▫ 每个属性独占一行
▫ 多个规则的分隔符`,`后
~~~
/* not good */
.element
{color: red; background-color: black;}
/* good */
.element {
color: red;
background-color: black;
}
/* not good */
.element, .dialog {
...
}
/* good */
.element,
.dialog {
...
}
~~~
# 注释
* 注释统一用`/* */`（scss中也不要用`//`），具体参照例子的写法；
* 缩进与下一行代码保持一致；
* 可位于一个代码行的末尾，与代码间隔一个空格。
~~~
/* Modal header */
.modal-header {
...
}
/*
* Modal header
*/
.modal-header {
...
}
.modal-header {
/* 50px */
width: 50px;
color: red; /* color red */
}
~~~
# 引号
* 最外层统一使用双引号；
* url的内容要用引号；
* 属性选择器中的属性值需要引号。
~~~
.element:after {
content: "";
background-image: url("logo.png");
}
li[data-type="single"] {
...
}
~~~
# 命名
* css 元素名称以及id和类名的命名也是**区分大小写**的（但是属性和值不区分）
* 类名使用小写字母，以中划线`-`分隔
* id采用驼峰式命名
* scss中的变量、函数、混合、placeholder采用驼峰式命名
~~~
/* class */
.element-content {
...
}
/* id */
#myDialog {
...
}
/* 变量 */
$colorBlack: #000;
/* 函数 */
@function pxToRem($px) {
...
}
/* 混合 */
@mixin centerBlock {
...
}
/* placeholder */
%myDialog {
...
}
~~~
# 属性声明顺序
* 相关的属性声明按例子的顺序做分组处理，组之间需要有一个空行。
~~~
.declaration-order {
display: block;
float: right;
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
z-index: 100;
border: 1px solid #e5e5e5;
border-radius: 3px;
width: 100px;
height: 100px;
font: normal 13px "Helvetica Neue", sans-serif;
line-height: 1.5;
text-align: center;
color: #333;
background-color: #f5f5f5;
opacity: 1;
}
// 下面是推荐的属性的顺序
[
[
"display",
"visibility",
"float",
"clear",
"overflow",
"overflow-x",
"overflow-y",
"clip",
"zoom"
],
[
"table-layout",
"empty-cells",
"caption-side",
"border-spacing",
"border-collapse",
"list-style",
"list-style-position",
"list-style-type",
"list-style-image"
],
[
"-webkit-box-orient",
"-webkit-box-direction",
"-webkit-box-decoration-break",
"-webkit-box-pack",
"-webkit-box-align",
"-webkit-box-flex"
],
[
"position",
"top",
"right",
"bottom",
"left",
"z-index"
],
[
"margin",
"margin-top",
"margin-right",
"margin-bottom",
"margin-left",
"-webkit-box-sizing",
"-moz-box-sizing",
"box-sizing",
"border",
"border-width",
"border-style",
"border-color",
"border-top",
"border-top-width",
"border-top-style",
"border-top-color",
"border-right",
"border-right-width",
"border-right-style",
"border-right-color",
"border-bottom",
"border-bottom-width",
"border-bottom-style",
"border-bottom-color",
"border-left",
"border-left-width",
"border-left-style",
"border-left-color",
"-webkit-border-radius",
"-moz-border-radius",
"border-radius",
"-webkit-border-top-left-radius",
"-moz-border-radius-topleft",
"border-top-left-radius",
"-webkit-border-top-right-radius",
"-moz-border-radius-topright",
"border-top-right-radius",
"-webkit-border-bottom-right-radius",
"-moz-border-radius-bottomright",
"border-bottom-right-radius",
"-webkit-border-bottom-left-radius",
"-moz-border-radius-bottomleft",
"border-bottom-left-radius",
"-webkit-border-image",
"-moz-border-image",
"-o-border-image",
"border-image",
"-webkit-border-image-source",
"-moz-border-image-source",
"-o-border-image-source",
"border-image-source",
"-webkit-border-image-slice",
"-moz-border-image-slice",
"-o-border-image-slice",
"border-image-slice",
"-webkit-border-image-width",
"-moz-border-image-width",
"-o-border-image-width",
"border-image-width",
"-webkit-border-image-outset",
"-moz-border-image-outset",
"-o-border-image-outset",
"border-image-outset",
"-webkit-border-image-repeat",
"-moz-border-image-repeat",
"-o-border-image-repeat",
"border-image-repeat",
"padding",
"padding-top",
"padding-right",
"padding-bottom",
"padding-left",
"width",
"min-width",
"max-width",
"height",
"min-height",
"max-height"
],
[
"font",
"font-family",
"font-size",
"font-weight",
"font-style",
"font-variant",
"font-size-adjust",
"font-stretch",
"font-effect",
"font-emphasize",
"font-emphasize-position",
"font-emphasize-style",
"font-smooth",
"line-height",
"text-align",
"-webkit-text-align-last",
"-moz-text-align-last",
"-ms-text-align-last",
"text-align-last",
"vertical-align",
"white-space",
"text-decoration",
"text-emphasis",
"text-emphasis-color",
"text-emphasis-style",
"text-emphasis-position",
"text-indent",
"-ms-text-justify",
"text-justify",
"letter-spacing",
"word-spacing",
"-ms-writing-mode",
"text-outline",
"text-transform",
"text-wrap",
"-ms-text-overflow",
"text-overflow",
"text-overflow-ellipsis",
"text-overflow-mode",
"-ms-word-wrap",
"word-wrap",
"-ms-word-break",
"word-break"
],
[
"color",
"background",
"filter:progid:DXImageTransform.Microsoft.AlphaImageLoader",
"background-color",
"background-image",
"background-repeat",
"background-attachment",
"background-position",
"-ms-background-position-x",
"background-position-x",
"-ms-background-position-y",
"background-position-y",
"-webkit-background-clip",
"-moz-background-clip",
"background-clip",
"background-origin",
"-webkit-background-size",
"-moz-background-size",
"-o-background-size",
"background-size"
],
[
"outline",
"outline-width",
"outline-style",
"outline-color",
"outline-offset",
"opacity",
"filter:progid:DXImageTransform.Microsoft.Alpha(Opacity",
"-ms-filter:\\'progid:DXImageTransform.Microsoft.Alpha",
"-ms-interpolation-mode",
"-webkit-box-shadow",
"-moz-box-shadow",
"box-shadow",
"filter:progid:DXImageTransform.Microsoft.gradient",
"-ms-filter:\\'progid:DXImageTransform.Microsoft.gradient",
"text-shadow"
],
[
"-webkit-transition",
"-moz-transition",
"-ms-transition",
"-o-transition",
"transition",
"-webkit-transition-delay",
"-moz-transition-delay",
"-ms-transition-delay",
"-o-transition-delay",
"transition-delay",
"-webkit-transition-timing-function",
"-moz-transition-timing-function",
"-ms-transition-timing-function",
"-o-transition-timing-function",
"transition-timing-function",
"-webkit-transition-duration",
"-moz-transition-duration",
"-ms-transition-duration",
"-o-transition-duration",
"transition-duration",
"-webkit-transition-property",
"-moz-transition-property",
"-ms-transition-property",
"-o-transition-property",
"transition-property",
"-webkit-transform",
"-moz-transform",
"-ms-transform",
"-o-transform",
"transform",
"-webkit-transform-origin",
"-moz-transform-origin",
"-ms-transform-origin",
"-o-transform-origin",
"transform-origin",
"-webkit-animation",
"-moz-animation",
"-ms-animation",
"-o-animation",
"animation",
"-webkit-animation-name",
"-moz-animation-name",
"-ms-animation-name",
"-o-animation-name",
"animation-name",
"-webkit-animation-duration",
"-moz-animation-duration",
"-ms-animation-duration",
"-o-animation-duration",
"animation-duration",
"-webkit-animation-play-state",
"-moz-animation-play-state",
"-ms-animation-play-state",
"-o-animation-play-state",
"animation-play-state",
"-webkit-animation-timing-function",
"-moz-animation-timing-function",
"-ms-animation-timing-function",
"-o-animation-timing-function",
"animation-timing-function",
"-webkit-animation-delay",
"-moz-animation-delay",
"-ms-animation-delay",
"-o-animation-delay",
"animation-delay",
"-webkit-animation-iteration-count",
"-moz-animation-iteration-count",
"-ms-animation-iteration-count",
"-o-animation-iteration-count",
"animation-iteration-count",
"-webkit-animation-direction",
"-moz-animation-direction",
"-ms-animation-direction",
"-o-animation-direction",
"animation-direction"
],
[
"content",
"quotes",
"counter-reset",
"counter-increment",
"resize",
"cursor",
"-webkit-user-select",
"-moz-user-select",
"-ms-user-select",
"user-select",
"nav-index",
"nav-up",
"nav-right",
"nav-down",
"nav-left",
"-moz-tab-size",
"-o-tab-size",
"tab-size",
"-webkit-hyphens",
"-moz-hyphens",
"hyphens",
"pointer-events"
]
]
~~~
# 颜色
* 使颜色16进制用小写字母；
* 颜色16进制尽量用简写。
~~~
/* not good */
.element {
color: #ABCDEF;
background-color: #001122;
}
/* good */
.element {
color: #abcdef;
background-color: #012;
}
~~~
# 属性简写
* 属性简写需要你非常清楚属性值的正确顺序，而且在大多数情况下并不需要设置属性简写中包含的所有值，所以建议尽量分开声明会更加清晰；
* margin 和 padding 相反，需要使用简写；
* 常见的属性简写包括：
▫ font
▫ background
▫ transition
▫ animation
~~~
/* not good */
.element {
transition: opacity 1s linear 2s;
}
/* good */
.element {
transition-delay: 2s;
transition-timing-function: linear;
transition-duration: 1s;
transition-property: opacity;
}
~~~
# 媒体查询
**尽量将媒体查询的规则被包含在他们相关的规则**，不要将他们一起放到一个独立的样式文件中，或者丢在文档的最底部，这样做只会让大家以后更容易忘记他们。
```css
// Example:
button {
font-size: 0.875rem;
// All the internal/external value use in 'em'
// This value use of your "font-size" as the basic font size
// And you will not have any problem with the font size of the container ( Example bottom )
padding: .5em 1em;
border: .125em solid #e3e3e3;
@media (min-width: 48rem){ // min-width: 768px
font-size: 1.125rem;
}
@media (min-width: 62rem){ // min-width: 992px
font-size: 1.375rem;
}
}
```
# 杂项
* 不允许有空的规则；
* 元素选择器用小写字母；
* **去掉小数点前面的0；**
* 去掉数字中不必要的小数点和末尾的0；
* **属性值`0`后面不要加单位；**
* 禁止使用`expression`表达式；
* 禁止滥用`!important`；
* 同个属性不同前缀的写法需要在垂直方向保持对齐，具体参照右边的写法；
* 无前缀的标准属性应该写在有前缀的属性后面；
~~~
-ms-transform:rotate(7deg); //-ms代表ie内核识别码
-moz-transform:rotate(7deg); //-moz代表火狐内核识别码
-webkit-transform:rotate(7deg); //-webkit代表谷歌内核识别码
-o-transform:rotate(7deg); //Opera15以前加 -o-，Opera15及以后加 -webkit-。
transform:rotate(7deg); //统一标识语句,符合w3c标准
~~~
* 不要在同个规则里出现重复的属性，如果重复的属性是连续的则没关系；
* 不要在一个文件里出现两个相同的规则；
* 用 `border: 0;` 代替 `border: none;`；
* 在保证选择器准确的情况下尽量简化选择器 (尽量不超过4级，最多4级)，不写多余的选择器(如class/id前的标签选择器、li上一级的的ul/ol、dt/dd上一级的dl等，在保证准确的前提下能去掉的都去掉)（在`scss`中如果超过4层应该考虑用嵌套的方式来写）；
* **尽量少用`*`选择器。**
~~~
/* not good */
.element {
}
/* not good */
LI {
...
}
/* good */
li {
...
}
/* not good */
.element {
color: rgba(0, 0, 0, 0.5);
}
/* good */
.element {
color: rgba(0, 0, 0, .5);
}
/* not good */
.element {
width: 50.0px;
}
/* good */
.element {
width: 50px;
}
/* not good */
.element {
width: 0px;
}
/* good */
.element {
width: 0;
}
/* not good */
.element {
border-radius: 3px;
-webkit-border-radius: 3px;
-moz-border-radius: 3px;
background: linear-gradient(to bottom, #fff 0, #eee 100%);
background: -webkit-linear-gradient(top, #fff 0, #eee 100%);
background: -moz-linear-gradient(top, #fff 0, #eee 100%);
}
/* good */
.element {
-webkit-border-radius: 3px;
-moz-border-radius: 3px;
border-radius: 3px;
background: -webkit-linear-gradient(top, #fff 0, #eee 100%);
background: -moz-linear-gradient(top, #fff 0, #eee 100%);
background: linear-gradient(to bottom, #fff 0, #eee 100%);
}
/* not good */
.element {
color: rgb(0, 0, 0);
width: 50px;
color: rgba(0, 0, 0, .5);
}
/* good */
.element {
color: rgb(0, 0, 0);
color: rgba(0, 0, 0, .5);
}
~~~
* 避免使用 @import语句。如果使用了@import语句，一定要将它们写在样式表开头，保证它的优先级低于样式表中的其他规则；与 `<link>` 标签相比，`@import` 指令要慢很多，不光增加了额外的请求次数，还会导致不可预料的问题。替代办法有以下几种：
▫ 使用多个 `<link>` 元素
▫ 通过 Sass 或 Less 类似的 CSS 预处理器将多个 CSS 文件编译为一个文件
▫ 通过 Rails、Jekyll 或其他系统中提供过 CSS 文件合并功能
▫ 请参考 http://www.stevesouders.com/blog/2009/04/09/dont-use-import/ 了解更多知识。
```html
<!-- Use link elements -->
<link rel="stylesheet" href="core.css">
<!-- Avoid @imports -->
<style>
@import url("more.css");
</style>
```
