css实用技巧——异步加载图片时，在图片完成加载前，鼠标悬浮到占位图片上时显示图片的alt信息

<template>
    <div style="padding: 20px">
        <img alt="我是一张苹果的照片">
    </div>
</template>
<style scoped>
    img {
        display: inline-block;
        width: 200px;
        height: 100px;
        /* 隐藏Firefox alt文字 */
        color: transparent;
        position: relative;
        overflow: hidden;
    }
 
    img:not([src]) {
        /* 隐藏Chrome alt文字以及银色边框 */
        visibility: hidden;
    }
 
    img::before {
        /* 淡蓝色占位背景 */
        content: "";
        position: absolute;
        left: 0;
        width: 100%;
        height: 100%;
        background-color: #f0f3f9;
        visibility: visible;
    }
 
    img::after {
        /* 黑色alt信息条 */
        content: attr(alt);
        position: absolute;
        left: 0;
        bottom: 0;
        width: 100%;
        line-height: 30px;
        background-color: rgba(0, 0, 0, .5);
        color: white;
        font-size: 14px;
        text-align: center;
        transform: translateY(100%);
        /* 来点过渡动画效果 */
        transition: transform .2s;
        visibility: visible;
    }
 
    img:hover::after {
        transform: translateY(0);
    }
</style>