add normalize.css

src/components/Preview.vue

@@ -19,6 +19,7 @@ function preview() {
     <title>预览</title>
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <style>${css.value}</style>
+    <link rel="stylesheet" href="/normalize.min.css" />
   </head>
   <body>
     ${html.value}