Update theme usage

src/lib/ThemeContext.svelte

@@ -2,10 +2,7 @@
     <script>
         if (document) {
             const defaultTheme = "dark";
-            const itemTheme = localStorage.getItem("theme") ?? defaultTheme;
-
-            localStorage.setItem("theme", itemTheme);
-            document.documentElement.setAttribute("data-theme", itemTheme);
+            document.documentElement.setAttribute("data-theme", defaultTheme);
         }
     </script>
 </svelte:head>

src/routes/+error.svelte

@@ -291,7 +291,6 @@ Still alive.</p>
 
 <style>
     * {
-        color: white !important;
         font-family: monospace;
         white-space: pre;
     }

src/routes/admin/+page.svelte

@@ -54,7 +54,7 @@
     }
 
     li a:hover {
-        border-bottom: 2px solid white;
+        border-bottom: 2px solid var(--link-color-hover);
     }
 
     h2 {