css - 显示背景图像的透明边框

Question

<分区>

Answer 1

您可以使用伪元素实现显示背景图像的透明边框。

红色背景是伪元素的边框，透明边框由元素背景和伪元素边框之间的间隙创建:

DEMO :

body{
    background:url('https://farm4.staticflickr.com/3771/13199704015_72aa535bd7.jpg');
    background-size:cover;
}
.big{
    margin:50px;
    padding:50px;
    min-height:500px;
    overflow:hidden;
}
.big p{
    position:relative;
    z-index:1;
}
.small{
    position:relative;
    background:teal;
    width:150px;height:150px;
    margin:25px;
    z-index:0;
}
.small:before{
    content:'';
    position:absolute;
    top:-5025px; left:-5025px;
    width:200px; height:200px;
    border:5000px solid rgba(255,255,255,0.8);
    background:none;
}

<div class="big">
    <p>content here</p>
    <div class="small"></div>
    <p>content here</p>
</div>

输出:

您还可以使用 box-shadow 而不是 border，这样您就不必为伪元素的 top/left 定位使用负值。浏览器支持 isn't as good作为边框:

body{
    background:url('https://farm4.staticflickr.com/3771/13199704015_72aa535bd7.jpg');
    background-size:cover;
}
.big{
    margin:50px;
    padding:50px;
    min-height:500px;
    overflow:hidden;
}
.big p{
    position:relative;
    z-index:1;
}
.small{
    position:relative;
    background:teal;
    width:150px;height:150px;
    margin:25px;
    z-index:0;
}
.small:before{
    content:'';
    position:absolute;
    top:-25px; left:-25px;
    width:200px; height:200px;
    box-shadow: 0px 0px 0px 5000px rgba(255,255,255,0.8);
    background:none;
}

<div class="big">
    <p>content here</p>
    <div class="small"></div>
    <p>content here</p>
</div>