Tailwind Upgrade 3.x -> 4.0

Tailwind 4.0 just dropped yesterday so I'm fine waiting on merging this
change to see if any issues shake out more generally.

The tailwind config file is no longer needed and it uses CSS config.
The CLI for tailwind is now a separate package.

I followed the upgrade guide/script for this upgrade:
https://tailwindcss.com/docs/upgrade-guide

Author: davidfischer

assets/src/input.css

@@ -1,4 +1,46 @@
-@tailwind base;
+@import 'tailwindcss';
+
+@utility container {
+  margin-inline: auto;
+  padding-inline: 1rem;
+  @media (width >= theme(--breakpoint-sm)) {
+    padding-inline: 2rem;
+  }
+  @media (width >= theme(--breakpoint-lg)) {
+    padding-inline: 4rem;
+  }
+  @media (width >= theme(--breakpoint-xl)) {
+    padding-inline: 6rem;
+  }
+  @media (width >= theme(--breakpoint-2xl)) {
+    padding-inline: 12rem;
+  }
+}
+
+/*
+  The default border color has changed to `currentColor` in Tailwind CSS v4,
+  so we've added these compatibility styles to make sure everything still
+  looks the same as it did with Tailwind CSS v3.
+
+  If we ever want to remove these styles, we need to add an explicit border
+  color utility to any element that depends on these defaults.
+*/
+@layer base {
+  *,
+  ::after,
+  ::before,
+  ::backdrop,
+  ::file-selector-button {
+    border-color: var(--color-gray-200, currentColor);
+  }
+}
+
+@utility btn {
+  @apply inline-flex items-center justify-center border align-middle select-none font-medium text-center hover:no-underline focus:no-underline focus:shadow-none text-sm py-2 px-4 shadow-xs hover:shadow-md bg-transparent hover:bg-slate-700 text-slate-700 hover:text-white rounded-sm;
+  svg {
+    @apply fill-current w-4 h-4 mr-2;
+  }
+}
 
 /* https://tailwindcss.com/docs/preflight#extending-preflight */
 /* https://tailwindcss.com/docs/adding-custom-styles#adding-base-styles */
@@ -37,15 +79,3 @@
     @apply mb-4;
   }
 }
-
-@tailwind components;
-@tailwind utilities;
-
-@layer components {
-  .btn {
-    @apply inline-flex items-center justify-center border align-middle select-none font-medium text-center hover:no-underline focus:no-underline focus:shadow-none text-sm py-2 px-4 shadow-sm hover:shadow-md bg-transparent hover:bg-slate-700 text-slate-700 hover:text-white rounded;
-    svg {
-      @apply fill-current w-4 h-4 mr-2;
-    }
-  }
-}