<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.banner {
position: relative;
margin: 0 auto;
width: 1226px;
height: 600px;
}
.mask {
position: absolute;
left: 0;
bottom: 0;
/* 绝对定位的盒子显示模式具备行内块特点: 加宽度高度生效, 如果没有宽度也没有内容, 盒子的宽度尺寸就是0 */
/* width: 1226px; */
/* 如果子级和父级的宽度相同 */
width: 100%;
height: 150px;
background-color: rgba(0,0,0, .5);
}
</style>
</head>
<body>
<div class="banner">
<img src="./images/bg.jpg" alt="">
<!-- 遮罩 -->
<div class="mask">111</div>
</div>
</body>
</html>
