> For the complete documentation index, see [llms.txt](https://jackmeng.gitbook.io/note/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jackmeng.gitbook.io/note/frontend/css/less.md).

# less

#### [less](http://lesscss.org/#)

less是一种动态样式语言,属于css预处理器的范畴,它扩展了 CSS 语言, 增加了变量、Mixin、函数等特性,使 CSS 更易维护和扩展 LESS既可以在客户端上运行 ,也可以借助Node.js在服务端运行

#### Less编译工具

[koala](http://koala-app.com/)

#### less中的注释

* 以//开头的注释,不会被编译到css文件中
* 以/\*\*/包裹的注释会被编译到css文件中

#### grammar

**variable**

**variable grammar**

```less
@width : 100px;
.w {
width: @width;
}
```

**variable scope**

```less
@width : 1px;
.meng {
	@width : 2px;
	.long {
		@width : 90px;
		width:@width;
		@width : 22px;
	}
	width: @width;
}
```

```less
.long {
  width: @w;
  @o: 9%;
}
@w: @o;
@o: 100%;
```

**字符串插值**

```less
@myUrl: "http://www.ibeifeng.com ";
.meng {
	background-image: url("@{myUrl}/images/bg.png");
}
```

**selector插值**

```less
@Myname: meng1314;
.@{Myname} {
  width:1000000000000px;
}
```

**media query as variable**

```less
@singleQuery: ~"(max-width: 768px)";
div {
	background-color: red;
}
@media screen and @singleQuery {
	div {
		background-color: blue;
	}
}
```

**variable引用variable**

```less
@meng : 5201314px;
@loveDay : meng;
div {
	width:@@loveDay;
}
```

**Mixins**

**继承类名**

```less
.width {
	width:1232px;
}
#height {
	height:2980px;
}
.long {
	.width;
	.meng {
		#height;
		.width;
	}
}
```

**带参数混合**

```less
.width (@width) {
	width:@width;
}
#height (@height) {
	height:@height;
}
.long {
	.width(20px);
	.meng {
		#height(30em);
		.width(50%);
	}
}
```

**隐藏属性继承**

```less
.width() {
	width:1234px;
}
#height() {
	height:5678px;
}
.long {
	.width();
	.meng {
		#height();
		.width();
	}
}
```

**默认值混合**

```less
.width (@width:2345px) {
	width:@width;
}
#height (@height:6789px) {
	height:@height;
}
.long {
	.width();
	#height(753px);
	.meng {
		#height();
		.width(951px);
	}
}
```

**多参数混合**

* 多个参数可以使用分号戒者逗号分隔,这里推荐使用分号分隔,因为逗号有 两重含义:它既可以表示混合的参数,也可以表示一个参数中一组值的分隔 符
* 使用分号作为参数分隔符意味着可以将逗号分隔的一组值作为一个变量处 理.换句话说,如果编译器在混合的定义戒者是调用中找到至少一个分号, 就会假设参数是使用分号分隔的,所有的逗号都属亍参数中的一组值的分隔 符
* 2 个参数,每个参数都含有通过逗号分隔的一组值的情况:`.name(1, 2, 3 ; something, else)`
* 3 个参数,每个参数叧含一个数字的情况:`.name(1, 2, 3)`
* 使用一个象征性的分号可以创建一个叧含一个参数,但参数包含一组值的混 合:`.name(1, 2, 3;)`
* 逗号分隔的一组值参数的默认值:`.name(@param1: red, blue;)`

```less
.mixin(@width) {
	width-1: @width;
}
.mixin(@width; @height:2em) {
	width-2: @width;
	height-2: @height;
}
.mixin(@width; @height; @margin: 2em) {
	width-3: @width;
	height-3: @height;
	margin: @margin @margin @margin @margin;
}
h1 {
	.mixin(red);
}
div {
	.mixin(#000,3px);
}
span {
	.mixin(#fff,3px,5px);
}
```

**@arguments**

```less
.transition (@moveStyle :all;@delayTime : 4s;@moveType : ease-in; @moveTime :
2s) {
	-webkit-transition: @arguments;
	-moz-transition: @arguments;
	-o-transition: @arguments;
	-ms-transition: @arguments;
	transition: @arguments;
}

div {
	.transition;
}
span {
	.transition (width);
}
h1 {
	.transition (height; 80s);
}
li {
	.transition (all; 80s; ease-out);
}
dd {
	.transition (color; 80s; ease-in-out; 30s);
}
```

**!important 关键字**

```less
.my (@width : 20px; @height : 50px){
	width:@width;
	height : @height;
}
.meng {
	.my;
}
.long {
	.my(40px);
}
.menglong {
	.my(234px; 299px);
}
.meng2 {
	.my !important;
}
.long2 {
	.my(40px) !important;
}
.menglong2 {
	.my(234px; 299px) !important;
}
```

**高级参数用法**

```less
/*接受 0-N 个参数*/
.mixin1 (...) {
	padding:@arguments;
}
div {
	.mixin1(20px);
	div {
		.mixin1(20px 30px);
			div {
				.mixin1(20px 50px 203px);
				div {
					.mixin1(20px 4px 4px 8px);
				}
			}
	}
}

/*不接受任何参数*/
.mixin2 () {
	height : 131px;
}
span {
.mixin2;
}
/*接受 0-1 个参数*/
.mixin3 (@a: #fff) {
	color : @a;
}
h1 {
	.mixin3;
	h2 {
		.mixin3(#eee);
	}
}

/*接受 0-N 个参数*/
.mixin4 (@a: 1, ...) {
	margin : @arguments;
}
a {
	.mixin4;
	span {
		.mixin4(32%,223em,231px,111px);
	}
}
/*接受 1-N 个参数*/
.mixin5 (@a, ...) {
	margin : @arguments;
}
.meng {
	.mixin5(90px);
	span {
		.mixin5(32%,223em,231px,111px);
	}
}
```

**模式匹配与 Guard 表达式**

```less
.mixin (dark, @color) {
	color: darken(@color, 10%);
}
.mixin (light, @color) {
	color: lighten(@color, 10%);
}
.mixin (@_, @color) {
	display: block;
}
@switch: light;
.long {
	.mixin(@switch, #888);
}
@switch2 : dark;
.meng {
	.mixin(@switch2, #666);
}
```

**也可以根据参数的数量迚行匹配**

```less
.mixin (@a) {
	color: @a;
}
.mixin (@a, @b) {
	color: fade(@a, @b);
}
.meng {
	.mixin(#000);
}
.long {
	.mixin(#fff, 10%);
}
```

**条件混合(guarded mixins)**

**通过 LESS 自带的函数判断**

```less
.mixin (@a) when (lightness(@a) >= 50%) {
	background-color: black;
}
.mixin (@a) when (lightness(@a) < 50%) {
	background-color: white;
}
.mixin (@a) {
	color: @a;
}
.meng {
	.mixin(#ddd);
}
.long {
	.mixin(#555);
}
```

**运算符判断**

Guards 支持的运算符包括:> >= = =< <.说明一下,true 关键字是唯 一被判断为真的值,也就是这两个混合是相等的

```less
@IE : true;
@w : 10;
.IE (@bTure) when (@bTure){
	*display:block;
}
.IE1 (@bTure) when (@bTure){
	*margin:0;
}
.IE2 (@bTure) when (@bTure >=0){
	*padding:@bTure;
}
.IE3 (@bTure) when (@bTure >0){
	*height:20px;
}
div {
	.IE(@IE);
	.IE1(@IE);
	.IE2(@w);
	.IE3(@w);
}
```

**多个条件**

多个 Guards 可以通过逗号表示分隔,如果其中任意一个结果为 true,则匹配成 功

```less
@IE : true;
@w : 10;
.IE (@bTure, @b) when (@bTure), (@b < -10){
	*display:block;
}
.IE1 (@bTure, @b) when (@bTure = false), (@b < -10){
	*width:20px;
}
.IE2 (@bTure, @b) when (@bTure = true), (@b < -10){
	*height:20px;
}
div {
	.IE(@IE, @w);
	.IE1(@IE, @w);
	.IE2(@IE, @w);
}
```

**参数间比较**

```less
@h : 20;
@w : 10;
.mixin (@h, @w) when (@h < @w){
	width:@h;
}
.mixin1 (@h, @w) when (@h > @w){
	height:@w;
}
div {
	.mixin(@h, @w);
	.mixin1(@h, @w);
}
```

**guard 中的 and**

```less
@h : 20;
@w : 10;
@true : true;
.mixin (@h, @w) when (@h > @w) and (@true) {
	width:@h;
}
div {
	.mixin(@h, @w);
}
```

**guard 中的 not**

```less
@h : 20;
.mixin (@h) when not(@h < 0) {
	width:@h;
}
div {
	.mixin(@h);
}
```

**嵌套语法**

```less
.meng { color: red;
	.long { font:bold 12px/20px "宋体"; }
	a {
		color:#000;
		span {padding: 10px;}
		i {
			width:10px;
			em {
				height : 90px;
			}
		}
	}
}
```

**&的用法**

& 符号的使用 — 如果你想写串联选择器,而不是写后代选择器,就可以用到 &了.这点对伪类尤其有用如 :hover 和 :focus

```less
.meng {
	color: red ;
	.long { font:bold 12px/20px "宋体" ; }
		a {
			color:#000;
			&:hover {
			text-decoration:none;
			}
			&:focus {
			color:#999;
			}
		}
		.menglong {
			background:red;
			&:hover {
				background:#777;
			}
	}
}
```

**&的高级用法**

```less
.meng, .long {
	div & {
		color: black ;
	}
	& + & {
		color: red;
	}
	& ~ & {
		color: red;
	}
}
```

**LESS 详解之命名空间**

```less
@height:100px;
.meng {
	.meng_button () {
		display: block;
		border: 1px solid black;
		background-color: grey;
		&:hover {
			background-color: white;
		}
	}
	.meng_tab () {
		height:@height
		width:100px;
	}
		.meng_citation () {
		@height:200px;
		height:@height
	}
}
div {
	.meng > .meng_tab;
}
h1 {
	.meng > .meng_citation;
}
```

#### function

**String**

* escape `escape('a=1') => a%3D1`
* e
* % format
* replace

**List**

* length
* extract
* range
* each

**Math**

* ceil、floor、round
* percentage
* sqrt、abs
* sin、asin、cos、acos、tan、atan
* pi、pow、mod
* min、max

**Type**

* isnumber
* isstring
* iscolor
* iskeyword
* isurl
* ispixel
* isem
* ispercentage
* isunit
* isruleset

**Misc**

* color
* convert
* data-uri
* default
* unit、getunit
* image-size、image-width、image-height
* svg-gradient

**Color series**

* rgb、rgba
* ....

**function & operation**

```less
@the-border: 1px;
@base-color: #111;
@red: #842210;
#header {
    color: @base-color * 3;
    border-left: @the-border;
    border-right: @the-border * 2;
}
#footer {
    color: @base-color + #003300;
    border-color: desaturate(@red, 10%);
}
```

#### example

```html
<!-- 以下大部分使用的html -->
<div id="somediv" style="width:200px;height:50;background-color:blue">
</div>
```

**简单的圆角半径**

```less
/* Mixin */
.border-radius (@radius: 5px) {
    -webkit-border-radius: @radius;
    -moz-border-radius: @radius;
    border-radius: @radius;
}
/* Implementation */
#somediv {
	.border-radius(20px);
}
```

**四角的半径定制**

```less
/* Mixin */
.border-radius-custom (@topleft: 5px, @topright: 5px, @bottomleft: 5px,
@bottomright: 5px) {
    -webkit-border-radius: @topleft @topright @bottomright @bottomleft;
    -moz-border-radius: @topleft @topright @bottomright @bottomleft;
    border-radius: @topleft @topright @bottomright @bottomleft;
}
/* Implementation */
#somediv {
	.border-radius-custom(20px, 20px, 0px, 0px);
}
```

**Box Shadow**

```less
/* Mixin */
.box-shadow (@x: 0px, @y: 3px, @blur: 5px, @alpha: 0.5) {
    -webkit-box-shadow: @x @y @blur rgba(0, 0, 0, @alpha);
    -moz-box-shadow: @x @y @blur rgba(0, 0, 0, @alpha);
    box-shadow: @x @y @blur rgba(0, 0, 0, @alpha);
}
/* Implementation */
#somediv {
	.box-shadow(5px, 5px, 6px, 0.3);
}
```

**Transition**

```less
/* Mixin */
.transition (@prop: all, @time: 1s, @ease: linear) {
    -webkit-transition: @prop @time @ease;
    -moz-transition: @prop @time @ease;
    -o-transition: @prop @time @ease;
    -ms-transition: @prop @time @ease;
    transition: @prop @time @ease;
}
/* Implementation */
#somediv {
	.transition(all, 0.5s, ease-in);
}
#somediv:hover {
	opacity: 0.5;
}
```

**Transform**

```less
/* Mixin */
.transform (@rotate: 90deg, @scale: 1, @skew: 1deg, @translate: 10px) {
    -webkit-transform: rotate(@rotate) scale(@scale) skew(@skew)
    translate(@translate);
    -moz-transform: rotate(@rotate) scale(@scale) skew(@skew)
    translate(@translate);
    -o-transform: rotate(@rotate) scale(@scale) skew(@skew)
    translate(@translate);
    -ms-transform: rotate(@rotate) scale(@scale) skew(@skew)
    translate(@translate);
    transform: rotate(@rotate) scale(@scale) skew(@skew) translate(@translate);
}
/* Implementation */
#someDiv {
	.transform(5deg, 0.5, 1deg, 0px);
}
```

**Linear Gradient**

```less
/* Mixin */
.gradient (@origin: to left, @start: #ffffff, @stop: #000000) {
    background-color: @start;
    background-image: -webkit-linear-gradient(@origin, @start, @stop);
    background-image: -moz-linear-gradient(@origin, @start, @stop);
    background-image: -o-linear-gradient(@origin, @start, @stop);
    background-image: -ms-linear-gradient(@origin, @start, @stop);
    background-image: linear-gradient(@origin, @start, @stop);
}
/* Implementation */
#someDiv {
	.gradient(to left, #663333, #333333);
}
```

**Quick Gradient**

```less
/* Mixin */
.quick-gradient (@origin: to left, @alpha: 0.2) {
    background-image: -webkit-linear-gradient(@origin, rgba(0,0,0,0.0),
    rgba(0,0,0,@alpha));
    background-image: -moz-linear-gradient(@origin, rgba(0,0,0,0.0),
    rgba(0,0,0,@alpha));
    background-image: -o-linear-gradient(@origin, rgba(0,0,0,0.0),
    rgba(0,0,0,@alpha));
    background-image: -ms-linear-gradient(@origin, rgba(0,0,0,0.0),
    rgba(0,0,0,@alpha));
    background-image: linear-gradient(@origin, rgba(0,0,0,0.0),
    rgba(0,0,0,@alpha));
}
/* Implementation */
#somediv {
background-color: #000000;
	.quick-gradient(to top, 0.2);
}
```

**Webkit Reflection**

```less
/* Mixin */
.reflect (@length: 50%, @opacity: 0.2){
    -webkit-box-reflect: below 0px -webkit-gradient(linear, left top, left bottom,
    from(transparent), color-stop(@length, transparent),
    to(rgba(255,255,255,@opacity)));
}
/* Implementation */
#somediv {
	.reflect(20%, 0.2);
}
```

**互补色方案**

```html
<!-- 以下使用的html -->
<div class="one" style="width:30px;height:100px;float:left"></div>
<div class="two" style="width:30px;height:100px;float:left"></div>
<div class="three" style="width:30px;height:100px;float:left"></div>
<div class="four" style="width:30px;height:100px;float:left"></div>
<div class="five" style="width:30px;height:100px;float:left"></div>
```

```less
/* Mixin */
@base: #663333;
@complement1: spin(@base, 180);
@complement2: darken(spin(@base, 180), 5%);
@lighten1: lighten(@base, 15%);
@lighten2: lighten(@base, 30%);
/* Implementation */
.one {background-color: @base;}
.two { background-color: @complement1;}
.three { background-color: @complement2;}
.four { background-color: @lighten1;}
.five { background-color: @lighten2;}
```

**颜色微调**

```less
/* Mixin */
@base: #663333;
@lighter1: lighten(spin(@base, 5), 10%);
@lighter2: lighten(spin(@base, 10), 20%);
@darker1: darken(spin(@base, -5), 10%);
@darker2: darken(spin(@base, -10), 20%);
/* Implementation */
.one {background-color: @base;}
.two { background-color: @lighter1;}
.three { background-color: @lighter2;}
.four { background-color: @darker1;}
.five { background-color: @darker2;}
```

**递归案例**

```less
//分析 1 - 奇数行为 PtzControl-*-out ,偶数行为 PtzControl-*- over
//分析 2 – 共 18 行,9 个迭代( 从 1 到 9 )
//分析 3 - background-position : A B,其中的 B -80 为一个递增引子
@cons:-80px;
.myLoop(@counter,@i:0) when (@i <@counter) {
    @c:@i+1;
    .PtzControl-@{c}-out {
    background-position: 0 @cons * (@i*2);
    }
    .PtzControl-@{c}-over {
    background-position: 0 @cons * (@i*2+1);
    }
    .myLoop(@counter,@i + 1); // next iteration
}
.myLoop(9);
```