feat(theme): persistent light/dark toggle in the titlebar

index.html

@@ -4,6 +4,16 @@
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <link rel="icon" type="image/png" href="/margin-mark.png" />
+    <script>
+      (function () {
+        try {
+          var t = localStorage.getItem("margin-theme");
+          if (t !== "light" && t !== "dark")
+            t = matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+          document.documentElement.setAttribute("data-theme", t);
+        } catch (e) {}
+      })();
+    </script>
     <title>margin</title>
   </head>
   <body>