add background design to better match wizard

html/error_page.html

@@ -6,22 +6,30 @@
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
     <style>
      :root {
-       --background-color: #fefefe;
-       --color: #010101;
+       --background-color: #dddddd;
+       --color: #222222;
+       --border-color: #bbbbbb;
        @media (prefers-color-scheme: dark) {
-         --color: #fefefe;
-         --background-color: #010101;
+         --color: #dddddd;
+         --border-color: #444444;
+         --background-color: #222222;
        }
      }
      body {
        font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
-    Oxygen-Sans, Ubuntu, Cantarell, Arial, sans-serif;
+       Oxygen-Sans, Ubuntu, Cantarell, Arial, sans-serif;
        background-color: var(--background-color);
        color: var(--color);
+       background-image: url(error-page-bg.png)
      }
      main {
        max-width: 800px;
        margin-inline: auto;
+       background-color: var(--background-color);
+       box-shadow: 0 4px 19px 6px rgba(0,0,0,.05);
+       padding: 1em;
+       border: 1px solid var(--border-color);
+       border-radius: 8px;
      }
      #loading {
        margin-top: 130px;
@@ -36,6 +44,7 @@
        height: 20px;
        display: inline-block;
        animation: 1s infinite alternate loading;
+       margin-bottom: 3em;
      }
      #loading > *:nth-child(2) {
        animation-delay: 0.15s;