作為 CSS 的一種擴充,Less 不僅完全相容 CSS 文法,而且連新增的特性也是使用 CSS 文法。這樣的設計使得學習 Less 很輕松,而且你可以在任何時候回退到 CSS。less檔案是以less作為檔案字尾名,HTML引用時可以像css那樣引用,如下:
<link rel="stylesheet/less" type="text/css" href="styles.less">
注意:本文描述的一切都是基于1.4.0版本,除非有特殊标明。
變量:
變量的作用就是把值定義在一個地方,然後在各處使用,這樣能讓代碼更易維護,如下:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
// Variables
@link-color: #428bca; // sea blue
// 用法
a:link {
color: @link-color;
}.widget {
color: #fff;
background: @link-color;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
上面代碼将顔色#428bca賦給一個變量@link-color,然後在color屬性中使用變量,對應的css如下:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
a:link {
color: #428bca;
}.widget {
color: #fff;
background: #428bca;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
變量不僅可以用在屬性值上,也可以用在選擇元素名,屬性名(1.6.0支援),url和import方法。如下:
選擇元素名:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
// Variables
@mySelector: banner;
// Usage
.@{mySelector} {
font-weight: bold;
line-height: 40px;
margin: 0 auto;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
編譯後為
.banner {
font-weight: bold;
line-height: 40px;
margin: 0 auto;
}
url:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
// Variables
@p_w_picpaths: "../img";
// 用法
body {
color: #444;
background: url("@{p_w_picpaths}/white-sand.png");
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
編譯後
body {
color: #444;
background: url("../img/white-sand.png");
}
@import:
// Variables
@themes: "../../src/themes";
// Usage
@import "@{themes}/tidal-wave.less";
@import "../../src/themes/tidal-wave.less";
屬性名:
@property: color;
.widget {
@{property}: #0ee;
background-@{property}: #999;
}
.widget {
color: #0ee;
background-color: #999;
}
變量的變量名也可以是變量,如下:
@fnord: "I am fnord.";
@var: "fnord";
content: @@var;
content: "I am fnord.";
延遲加載:
變量支援延遲加載,是以你可以在變量定義之前使用。如下:
.lazy-eval {
width: @var;
}@var: @a;
@a: 9%;
或者
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.lazy-eval-scope {
width: @var;
@a: 9%;
}@var: @a;
@a: 100%;
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
上面兩個都會被編譯成如下
.lazy-eval-scope {
width: 9%;
}
問什麼第二個也會被編譯成上面的css,這是因為當一個變量被定義兩次時,最後一次定義的生效。就類似于css中,對同一個元素定義不同的css樣式,最後定義的生效。再比如下面這個
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
@var: 0;
.class1 {
@var: 1;
.class {
@var: 2;
three: @var;
@var: 3;
}
one: @var;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.class1 .class {
three: 3;
}.class {
one: 1;
}
Extend:
擴充選擇器是less的僞類選擇器,他會複制目前選擇器,定義新的樣式,而原來的不便
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
nav ul {
&:extend(.inline);
background: blue;
}.inline {
color: red;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
nav ul {
background: blue;
}.inline,
nav ul {
color: red;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
文法:
.a:extend(.b) {}也可以這樣使用
.a {
&:extend(.b);
}
.e:extend(.f) {}.e:extend(.g) {}// 上面等價于下面
.e:extend(.f, .g) {}
嵌套選擇器:
.bucket {
tr {
color: blue;
}}
.some-class:extend(.bucket tr) {}
.bucket tr,
.some-class {
color: blue;
}
精确比對:
.a.class,
.class.a,
.class > .a {
color: blue;
}.test:extend(.class) {} // 不會比對任何選擇
nth:
:nth-child(1n+3) {
color: blue;
}.child:extend(n+3) {}
:nth-child(1n+3) {
color: blue;
}
注意:1n+3與n+3在css中是等價的,但是在less中不等價。
屬性選擇器:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
[title=identifier] {
color: blue;
}[title='identifier'] {
color: blue;
}[title="identifier"] {
color: blue;
}.noQuote:extend([title=identifier]) {}.singleQuote:extend([title='identifier']) {}.doubleQuote:extend([title="identifier"]) {}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
[title=identifier],
.noQuote,
.singleQuote,
.doubleQuote {
color: blue;
}[title='identifier'],
.noQuote,
.singleQuote,
.doubleQuote {
color: blue;
}[title="identifier"],
.noQuote,
.singleQuote,
.doubleQuote {
color: blue;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
注意:less中不區分單引号雙引号
關鍵字all:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.a.b.test,
.test.c {
color: orange;
}.test {
&:hover {
color: green;
}}
.replacement:extend(.test all) {}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.a.b.test,
.test.c,
.a.b.replacement,
.replacement.c {
color: orange;
}.test:hover,
.replacement:hover {
color: green;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
變量選擇器:
@variable: .bucket;
@{variable} { // interpolated selector
color: blue;
}.some-class:extend(.bucket) {}// 不會比對任何選擇元素
.bucket {
color: blue;
}.some-class:extend(@{variable}) {} // 不會比對任何元素
@variable: .bucket;
注意:extend不比對變量。
@media:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
@media print {
.screenClass:extend(.selector) {} // extend inside media
.selector {
color: black;
}}
.selector {
color: red;
}@media screen {
.selector {
color: blue;
}}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
@media print {
.selector,
.screenClass {
color: black;
}}
.selector {
color: red;
}@media screen {
.selector {
color: blue;
}}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
注意:extend隻能比對@media中前面定義的,在後面定義的将忽略。
使用extend重寫樣式:
在開發中我們會定義一些通用樣式,然後單獨樣式在添加class,使用css的後面覆寫前面的原理來實作樣式。extend也可以實作這種效果,如下:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.animal {
background-color: black;
color: white;
}.bear {
&:extend(.animal);
background-color: brown;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
減少css代碼:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.my-inline-block() {
display: inline-block;
font-size: 0;
}.thing1 {
.my-inline-block;}.thing2 {
.my-inline-block;}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
編譯後:
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.thing1 {
display: inline-block;
font-size: 0;
}.thing2 {
display: inline-block;
font-size: 0;
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
使用extend
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.my-inline-block {
display: inline-block;
font-size: 0;
}.thing1 {
&:extend(.my-inline-block);
}.thing2 {
&:extend(.my-inline-block);
}
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsIiZpdmLlR2bjlHcvN2LcNHa0FGcjlGcfd3Xw9CXt92YuM3ZvxmYuNmLu9Wbt92Yvw1LcpDc0RHaiojIsJye.gif)
.my-inline-block,
.thing1,
.thing2 {
display: inline-block;
font-size: 0;
}