【前端笔记】CSS预处理语言 LESS

官网： Less 快速入门 | Less.js 中文文档 - Less 中文网

LESS很多地方可以比CSS简写很多

安装

npm install -g less

核心优势：变量、嵌套、混合、运算功能让CSS更容易维护，比原生CSS更加简洁高效

1. 变量（Variables）

@primary-color: #428bca;
@padding: 15px;

.header {
  background: @primary-color;
  padding: @padding;
}

2. 嵌套（Nesting）

.nav {
  ul {
    margin: 0;
    li {
      display: inline-block;
      a {
        color: #333;
      }
    }
  }
}

3. 混合（Mixins）

.border-radius(@radius: 5px) {
  border-radius: @radius;
}

.button {
  .border-radius();
  &.large {
    .border-radius(10px);
  }
}

4. 运算（Operations）

@base-width: 100px;
@padding: 20px;

.container {
  width: @base-width + @padding * 2;
}

内置函数重点

简单的示例之后是按照使用频率提取出来重点

数学函数（Math Functions）

@number: 3.14;

div {
  width: ceil(@number);    // 4
  height: floor(@number);  // 3
  line-height: round(@number); // 3
  margin: percentage(0.5); // 50%
}

颜色函数（Color Functions）

@color: #428bca;

a {
  color: lighten(@color, 20%);
  &:hover {
    color: darken(@color, 10%);
  }
}

字符串函数（String Functions）

@url: "image.png?size=large";

div {
  background: escape(@url); // 编码URL
}

列表函数（List Functions）

@list: "Arial", "Helvetica", sans-serif;

body {
  font-family: extract(@list, 2); // Helvetica
}

css1. 列表函数实战 - 生成间距系统

// 定义间距列表
@spacings: 4px, 8px, 12px, 16px, 24px;

// 自动生成工具类
each(@spacings, {
  .m-@{index} {
    margin: @value;
  }
  .p-@{index} {
    padding: @value;
  }
});

​​CSS运行逻辑：

.m-1 { margin: 4px; }
.p-1 { padding: 4px; }
.m-2 { margin: 8px; }
/* 其他省略... */

类型检查函数（Type Functions）

@value: #fff;

div {
  @if(iscolor(@value)) {
    color: @value;
  }
}

逻辑控制（Conditionals）

@theme: dark;

.header {
  @if (@theme = dark) {
    background: #333;
    color: #fff;
  } @else {
    background: #fff;
    color: #333;
  }
}

类型检查+逻辑控制 - 安全混合

// 安全的颜色混合函数
.safe-mix(@c1, @c2, @weight) when (iscolor(@c1)) and (iscolor(@c2)) {
  color: mix(@c1, @c2, @weight);
}

// 使用示例
.error-text {
  .safe-mix(red, "notacolor", 50%); // 不会生效（因为第二个参数不是颜色）
}

循环（Loops）

.generate-columns(4);

.generate-columns(@n, @i: 1) when (@i <= @n) {
  .column-@{i} {
    width: (@i * 100% / @n);
  }
  .generate-columns(@n, (@i + 1));
}

实战

这是之前写的一段CSS的代码，

.container{
    width:90%;
    max-width:1100px;
    margin:auto;
}
.main-nav{
    display:flex;
    align-items: center;
    justify-content: space-between;
    height: 60px;
    padding: 10px;
    font-size:13px;
}
.main-nav .logo{
    width:110px;
}

.main-nav ul{
    list-style-type: none; /* 去除无序列表的项目符号 */
    display:flex;
}
.main-nav ul li{
    padding: 0 10px;
}
.main-nav ul li a{
    padding-bottom: 2px;
    text-decoration: none;
    color: #333;
}
.main-nav ul li a:hover{
    border-bottom: 2px solid #000000;
}
.main-nav ul.main-menu{
    flex:1;
    margin-left: 20px;
}
.menu-btn{
    cursor:pointer;
    position:absolute;
    top:10px;
    right:30px;
    z-index:2;
    display:none;
}
.btn{
    cursor:pointer;
    display:inline-block;
    border:0;
    font-weight:bold;
    padding: 10px 20px;
    background: #262626;
    color:#fff;
    font-size:15px;
    text-decoration: none;;
}
.btn:hover{
    opacity:0.9;
}
.dark{
    color:#fff;
}
.dark .btn{
    background: #f4f4f4;
    color:#333;;
}

.showcase{
    width:100%;
    height:400px;
    background:url('https://i.ibb.co/zGSDGCL/slide1.png') no-repeat center center/cover;
    display:flex;
    flex-direction:column;
    justify-content:flex-end;
    align-items:center;
    text-align:center;
  
    padding-bottom: 50px;
    margin-bottom:20px;
}

.showcase h2, .showcase p{
    margin-bottom:10px;
}
.showcase .btn{
    margin-bottom:10px;
}

.home-cards{
    display:flex;
    grid-template-columns: repeat(4,1fr);
    grid-gap:10px;
    margin-bottom: 40px;
}

.home-cards img{
    width:100%;
    height: auto; /* 保持图片的宽高比 */
    object-fit: cover; /* 使图片完全覆盖容器，可能会裁剪图片 */
    margin-bottom:20px;
}

.home-cards h3{
    margin-bottom:5px;
}
.home-cards a{
    display:inline-block;
    padding-top:10px;
    font-weight:bold;
    color:#0067b8;
    text-transform:uppercase;
}
.home-cards a:hover{
    margin-left:10px;
}

.xbox{
    width:100%;
    height: 350px;
    background:url('https://i.ibb.co/tBJGPD9/xbox.png') no-repeat center center/cover;
    margin-bottom:20px;
    display:flex;
    flex-direction:column;
    justify-content:center;
}

.xbox .content{
    width:40%;
    padding:50px 0 0 30px;
}

.xbox p,carbon p{
    margin:10px 0 20px
}

.carbon{
    width:100%;
    height:350px;
    background:url('https://i.ibb.co/zVqhWn2/card5.png') no-repeat center center/cover;
    margin-bottom:20px;
    display:flex;
}
.carbon .content{
    width:40%;
    margin-left:20px;
    margin-top:20px;
}
.carbon .btn{
    margin-top:30px;
}
.links .links-inner {
    background: #f4f4f4;
    display:grid;
grid-template-columns: repeat(5, 1fr);
}

@media(max-width: 500px) {
.home-cards {
grid-template-columns: 1fr;
}

.links .links-inner {
grid-template-columns: 1fr;
}

.links .links-inner ul {
margin-bottom: 20px;
}
}

用less优化

@container-width: 90%;
@container-max-width: 1100px;
@nav-height: 60px;
@nav-padding: 10px;
@nav-font-size: 13px;
@logo-width: 110px;
@menu-margin-left: 20px;
@btn-padding: 10px 20px;
@btn-font-size: 15px;
@showcase-height: 400px;
@xbox-height: 350px;
@carbon-height: 350px;
@grid-gap: 10px;
@hover-transition: all 0.3s ease;

.flex-center(){
    display:flex;
    align-items:center;
    justify-content:center;
}
.flex-between() {
    display: flex;
    align-items: center;
    justify-content: space-between;
  }
  
  .background-cover() {
    background-repeat: no-repeat;
    background-position: center center;
    background-size: cover;
  }
  
  // 基础样式
  .container {
    width: @container-width;
    max-width: @container-max-width;
    margin: auto;
  }
  
  // 导航栏样式
  .main-nav {
    .flex-between();
    height: @nav-height;
    padding: @nav-padding;
    font-size: @nav-font-size;
  
    .logo {
      width: @logo-width;
    }
  
    ul {
      list-style-type: none;
      display: flex;
  
      li {
        padding: 0 10px;
  
        a {
          padding-bottom: 2px;
          text-decoration: none;
          color: #333;
          transition: @hover-transition;
  
          &:hover {
            border-bottom: 2px solid #000;
          }
        }
      }
  
      &.main-menu {
        flex: 1;
        margin-left: @menu-margin-left;
      }
    }
  }

  .btn{
    cursor:pointer;
    display:inline-block;
    padding:@btn-padding;
    background:#fff;
    font-size:@btn-font-size;
    text-decoration:none;
    transition:@hover-transition;

    &:hover{
        opacity:0.9;
    }
  }

  .dark{
    color:#fff;

    .btn{
        background:#f4f4f4;
        color:#333;

    }
  }

  .showcase{
    width:100%;
    height:@showcase-height;
    .background-cover();
    background-image: url('https://i.ibb.co/zGSDGCL/slide1.png');
    .flex-center();
    flex-direction: column;
    justify-content: flex-end;
    text-align: center;
    padding-bottom: 50px;
    margin-bottom: 20px;

    h2,p{
        margin-bottom:10px;
    }
    .btn{
        margin-bottom: 10px;
    }
  }

  .home-cards{
    display:grid;
    grid-template-columns: repeat(4, 1fr) ;
    gap:@grid-gap;
    margin-bottom:40px;

    img{
        width:100%;
        height: auto;
        object-fit: cover;
        margin-bottom: 20px;
    }

    h3{
        margin-bottom: 5px;
    }
    a{
        display:inline-block;
        padding-top:10px;
        font-weight:bold;
        color:#0067b8;
        text-decoration:none;
        text-transform: uppercase;
        transition:@hover-transition;

        &:hover{
            margin-left:10px;
        }

    }

}
.xbox {
    width: 100%;
    height: @xbox-height;
    .background-cover();
    background-image: url('https://i.ibb.co/tBJGPD9/xbox.png');
    margin-bottom: 20px;
    .flex-center();
    flex-direction: column;
  
    .content {
      width: 40%;
      padding: 50px 0 0 30px;
    }
  
    p, .carbon p {
      margin: 10px 0 20px;
    }
  }
  
  // Carbon 区域
  .carbon {
    width: 100%;
    height: @carbon-height;
    .background-cover();
    background-image: url('https://i.ibb.co/zVqhWn2/card5.png');
    margin-bottom: 20px;
    display: flex;
  
    .content {
      width: 40%;
      margin-left: 20px;
      margin-top: 20px;
    }
  
    .btn {
      margin-top: 30px;
    }
  }
  
  // 链接区域
  .links {
    .links-inner {
      background: #f4f4f4;
      display: grid;
      grid-template-columns: repeat(5, 1fr);
    }
  }
  
  // 响应式设计
  @media (max-width: 500px) {
    .home-cards {
      grid-template-columns: 1fr;
    }
  
    .links {
      .links-inner {
        grid-template-columns: 1fr;
  
        ul {
          margin-bottom: 20px;
        }
      }
    }
  }
  
  // 菜单按钮
  .menu-btn {
    cursor: pointer;
    position: absolute;
    top: 10px;
    right: 30px;
    z-index: 2;
    display: none;
  }
  
  

实现成功