图片放进去时，是正常的大小，设置宽度为50%时，图片为什么反而变大了呢
```bash
<!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>
<link rel="stylesheet" href="./css/reset.css">
<style>
/* .d1{
width: 100%;
display: flex;
justify-content: space-between;
align-items: center;
} */
.d1 a img {
width: 50%;
margin-left: 30px;
}
/* .d1 span{
margin-right: 30px;
} */
</style>
</head>
<body>
<div class="d1">
<a href=""><img src="./image1/login_back.png" alt=""></a>
<a href=""><span>登录</span></a>
</div>
</body>
</html>
```
