伪元素 Before & Aster

1. html 结构

  <label class="is-required" for="name">姓名</label>
  <input type="text">
  <header>
    <h1>欢迎来到米修在线</h1>
    <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Totam labore qui ut excepturi, accusamus, dolores soluta porro quae earum delectus rem neque, culpa ab nostrum aut est! Molestiae, nobis rem?</p>
    <h3>Lorem ipsum dolor sit amet.</h3>
    <p>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Expedita asperiores adipisci deleniti quibusdam voluptate debitis soluta assumenda sit aspernatur aperiam?</p>
  </header>

2. css 样式

body {
      font-family: Arial, Helvetica, sans-serif;
      background-color: #333;
      color: #fff;
      margin: 0;
    }
    header {
      display: flex;
      flex-direction: column;
      justify-content: center;
      text-align: center;
      align-items: center;
      height: 100vh;
    }
    header:before {
      background: url('https://images.pexels.com/photos/3294254/pexels-photo-3294254.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500') no-repeat center center/cover;
      opacity: 0.4;
      content: '';
      position: absolute;
      width: 100%;
      height: 100%;
      z-index: -1;
    }
    header > h1 {
      font-size: 4rem;
      margin: 1rem;
    }
    /* 设置必填项 */
    .is-required:after {
      content: '*';
      color: red;
      padding: 2px;
    }
    /* 在文本前 */
    .is-required:before {
      content: '*';
      color: red;
      padding: 2px;
    }

3. 重点

如果你想给一个input设置必填项 就在他的后面加上

.is-required:after {

      content: '*';

}

如果想加到文本的前面就把 after 改为 before

给父元素加上笼罩层

header:before {

      background: url('https://images.pexels.com/photos/3294254/pexels-photo-3294254.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500') no-repeat center center/cover;  

      opacity: 0.4;

      content: '';

      position: absolute;

      width: 100%;

      height: 100%;

      z-index: -1;

    }