Base: Support dark mode in directory page

Base/res/ladybird/templates/directory.html

@@ -4,6 +4,17 @@
     <meta charset="UTF-8">
     <title>Index of %path%</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);
+            }
+            a {
+                color: cornflowerblue;
+            }
+        }
+
         header {
             margin-bottom: 10px;
         }