border绘制与color变色实例页面可以看到，使用 border 实现，我们 hover 变色的时候，只需要重置 1

<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>
</head>

<body>
    <a href class="add" title="继续上传">
        添加图片
    </a>
</body>
<style>
    .add {
        display: inline-block;
        width: 76px;
        height: 76px;
        color: #ccc;
        border: 2px dashed;
        text-indent: -12em;
        transition: color .25s;
        position: relative;
        overflow: hidden;
    }

    .add:hover {
        color: #34538b;
    }

    .add::before,
    .add::after {
        content: '';
        position: absolute;
        top: 50%;
        left: 50%;
    }

    .add::before {
        width: 20px;
        border-top: 4px solid;
        margin: -2px 0 0 -10px;
    }

    .add::after {
        height: 20px;
        border-left: 4px solid;
        margin: -10px 0 0 -2px;
    }
</style>

</html>