了解sass

$font_size: 12px;
.container{
    font-size: $font_size;
}

$side : left;
.rounded {
    border-#{$side}: 1px solid #000;
}

.container{
    display: none;
    .header{
        width: 100%;
    }
}

```javascript
.container {
    border: {
        width: 1px;
    }
}

.link{
    &:hover{ 
        color: green;
    }  
}

// mixin
@mixin focus_style {
    outline: none;
}
div {
    @include focus_style; 
}

div {
  outline: none; }

// 参数、缺省值
@mixin the_height($h: 200px) {
        height: $h;
}
.box_default {
        @include the_height;
}
.box_not_default{
        @include the_height(100px);
}

.box_default {
  height: 200px; }

.box_not_default {
  height: 100px; }

// 继承
.class1{
        float: left;
}
.class2{
        @extend .class1;
        width: 200px;
}

.class1, .class2 {
  float: left; }

.class2 {
  width: 200px; }

.container{
        position: relative;
        height: (200px/2);
        width: 100px + 200px;
        left: 50px * 2;
        top: 50px - 10px;
}

.container {
  position: relative;
  height: 100px;
  width: 300px;
  left: 100px;
  top: 40px; }

@import "outer.scss";

@import "outer.css";

@function higher($h){
        @return $h * 2;
}
.container{
        height: higher(100px);
}

.container {
  height: 200px; }

// 单行注释，编译后消失

/* 标准的CSS注释，会保留到编译后的代码中 */

/*!
重要注释，压缩编译也不会消失
*/