Base: Support dark mode in error page

Base/res/ladybird/templates/error.html

@@ -4,6 +4,14 @@
     <meta charset="UTF-8">
     <title>Error!</title>
     <style>
+        /* FIXME: We should be able to remove the HTML style when "color-scheme" is supported */
+        @media (prefers-color-scheme: dark) {
+            html {
+                background-color: rgb(20, 20, 20);
+                color: rgb(235, 235, 235);
+            }
+        }
+
         h1 {
             display: inline;
         }