feat(ui): create idiomatic UI matching previous katbin iteration

Signed-off-by: SphericalKat <amolele@gmail.com>

lib/ketbin_web/templates/layout/app.html.eex

@@ -11,7 +11,7 @@
     <link href="https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;500;600;700;800&display=swap" rel="stylesheet">
     <script defer type="text/javascript" src="<%= Routes.static_path(@conn, "/js/app.js") %>"></script>
   </head>
-  <body>
+  <body class="flex flex-col ">
     <header class="flex w-full justify-between items-center py-3 px-6">
      <a href="<%= Routes.page_path(@conn, :index) %>">
         <span class="font-semibold text-xl tracking-tight">