[Tunny]CSS LESS Framework Basics_html/css_WEB-ITnose

[黄英?/Tunny,20140711]

Less is a Css precompiler, which means it can extend the Css language and add functions such as allowing variables (variables) , mixins, functions, and many other techniques can make CSS more maintainable, themed, and scalable.

This article is an introduction to Less and a syntax review. It includes some entry-level examples and is suitable for developers who have an entry-level understanding of Less.

The LESS source file is introduced in the same way as the standard CSS file:

<link rel="stylesheet/less" type="text/css" href="styles.less">

In the HTML where we need to introduce the LESS source file Add the following code:

<script src="less.js" type="text/javascript"></script>

Import file:

@import “variables.less”;@import “variables.css”;/*也可以将标准的 CSS 文件直接改成 .less 格式*/

Variables and Scope

 /*用变量管理值*/ @width : 20px; //全局变量 #homeDiv { #centerDiv{ width : @width; // 此处应该取最近定义的变量 width 的值 30px  } @width : 30px; //局部变量，变量和混合是延迟加载的，不一定要在使用前声明 } #leftDiv { width : @width; // 此处应该取最上面定义的变量 width 的值 20px  } /*用变量管理选择器名称、URLs、属性*/ @mySelector: banner; // 定义一个变量用于选择器名称 @images: "../img"; // 变量可以是字符串 @property: color; // 定义一个变量用于属性名称 .@{mySelector} { //选择器名称使用变量的用法 background: url("@{images}/white-sand.png");  //URLs使用变量的用法 @{property}: #0ee; …… //其它常规属性等 } /*编译生成的CSS文件*/ .banner { background: url("../img/white-sand.png"); color: #0ee; …… }

Variables can be defined and used in nested form

@fnord:  "I am fnord.";@var:    "fnord";content: @@var;//嵌套使用content: "I am fnord."; //编译后结果/*当一个变量定义两次时，只会使用最后定义的变量，Less会从当前作用域中向上搜索。*/

Numbers, colors and variables can be operated on

@init: #111111;@transition: @init*2;@var: 1px + 5 // Less能够判断颜色和单位之间的区别.switchColor { color: @transition; } /*编译生成的CSS文件*/ .switchColor { color: #222222; }

Mixins and functions

 .roundedCorners(@radius:5px) { //定义参数并且给予默认值 -moz-border-radius: @radius; -webkit-border-radius: @radius; border-radius: @radius;  } // 在另外的样式选择器中使用 #header { .roundedCorners; //使用类并且参数为默认值  } #footer { .roundedCorners(10px); //自定义参数值  } .bordered { border-top: dotted 1px black; border-bottom: solid 2px black; } #menu a { color: #111; .bordered; /*在另一个规则集内部使用上面类的属性，则直接访问属性所在类名（或Id名）即可*/ }

@arguments variable: When Mixins refers to this parameter, this parameter represents all variables (multiple parameters).

 .boxShadow(@x:0,@y:0,@blur:1px,@color:#000){ -moz-box-shadow: @arguments; -webkit-box-shadow: @arguments; box-shadow: @arguments;  } #header { .boxShadow(2px,2px,3px,#f36);  }

Namespace

#mynamespace { .home {...} .user {...} } //如果我们要复用 user 这个选择器的时候，我们只需要在需要混入这个选择器的地方这样使用就可以了。#mynamespace > .user

Nested Rules

<!-- HTML片段--> <div id="home"> <div id="top">top</div> </div>

/*使用嵌套规则的LESS 文件*/ #home{ color : blue; width : 600px; height : 500px; border:outset; #top{ border:outset; width : 90%;  } } /*编译生成的CSS文件*/ #home { color: blue; width: 600px; height: 500px; border: outset;  } #home #top { border: outset; width: 90%;  } a { color: red; text-decoration: none; &:hover { /*有 & 时解析的是同一个元素或此元素的伪类，没有 & 解析是后代元素，&表示当前选择器的父选择器*/ color: black; text-decoration: underline;  } } /*编译生成的CSS文件*/ a { color: red; text-decoration: none;  } a:hover { color: black; text-decoration: underline;  }

Extend

extend is a Less pseudo-class, which is an extension selector; the extension selector must At the end of all pseudo-classes

nav ul:extend(.inline)    background: blue;}.inline { color: red; } /*编译生成的CSS文件*/ nav ul { // 声明块保持原样 background: blue; } .inline,nav ul { color: red; } pre:hover , .some-class { &:extend(div pre); } /*以上与给每个选择器添加一个extend完全相同*/ pre:hover:extend(div pre), .some-class:extend(div pre) {}

essentially extend looks for the compiled CSS instead of the original less

.bucket { tr & { // 目标选择器中的嵌套，&代表最近父元素 color: blue;  } } .some-class:extend(tr .bucket) {} // 识别嵌套规则 /*编译生成的CSS文件*/ tr .bucket , .some-class { color: blue; }

extend must be an exact match (including wildcard *, pseudo-class order, nth expression, the only exception is the quotes in the attribute selector, less will know that they are the same and then match it)

.a.class,.class.a,.class > .a { color: blue; } .test:extend(.class) {} // 不会匹配上面的任何选择器的值 *.class { color: blue; } .noStar:extend(.class) {} //不会匹配*.class选择器 link:hover:visited { color: blue; } .selector:extend(link:visited:hover) {} //不会匹配，伪类顺序不同 :nth-child(1n+3) { color: blue; } .child:extend(n+3) {} //不会匹配，尽管逻辑上1n+3与n+3是相同的

[Version v2.0]

Huang Ying?/Tunny Wong:

v1.0 published on 2014-07-11

2014-07-13 First update v2.0