update tailwind v4, remove sass and postcss dependency

assets/css/main.css

@@ -0,0 +1,37 @@
+@import "tailwindcss";
+@plugin "@tailwindcss/forms";
+@plugin "@tailwindcss/typography";
+@plugin "./tailwind-plugin/tw-theme";
+@plugin "./tailwind-plugin/tw-bs-grid";
+@source "hugo_stats.json";
+
+@custom-variant dark (&:where(.dark, .dark *));
+
+@import "./safe.css";
+
+@layer base {
+  @import "./base.css";
+}
+
+@layer components {
+  @import "./components.css";
+  @import "./navigation.css";
+  @import "./buttons.css";
+}
+
+@layer utilities {
+  @import "./utilities.css";
+}
+
+@import "search.css";
+@import "social-share.css";
+@import "gallery-slider.css";
+@import "images.css";
+@import "toc.css";
+@import "tab.css";
+@import "accordion.css";
+@import "modal.css";
+@import "notice.css";
+
+@import "module-overrides.css";
+@import "custom.css";