Add DevBanner

src/lib/DevBanner.svelte

@@ -0,0 +1,19 @@
+<div id="banner">DEVMODE</div>
+
+<style>
+    #banner {
+        width: 200px;
+        background: red;
+        color: #fff;
+        position: fixed;
+        text-align: center;
+        top: 25px;
+        line-height: 40px;
+        right: -50px;
+        left: auto;
+        -ms-transform: rotate(45deg);
+        -webkit-transform: rotate(45deg);
+        transform: rotate(45deg);
+        z-index: 100;
+    }
+</style>

src/routes/+layout.svelte

@@ -1,5 +1,7 @@
 <script>
   import '../app.css';
+  import { dev } from '$app/environment';
+  import DevBanner from '$lib/DevBanner.svelte';
 </script>
 
 <svelte:head>
@@ -14,4 +16,7 @@
   <link rel="manifest" href="/manifest.json" />
   <title>OwlBoard</title>
 </svelte:head>
+{#if dev}
+    <DevBanner />
+{/if}
 <slot />