Refactor styles and remove Tailwind configuration

- Deleted postcss.config.mjs as it is no longer needed.
- Updated Layout.astro to reference main.css instead of using @tailwind components.
- Modified expressive-code.css to include a reference to Tailwind CSS.
- Reworked main.css to use @import for Tailwind and added custom variants and utilities.
- Updated markdown.css to reference main.css and adjusted anchor styles.
- Enhanced photoswipe.css and scrollbar.css with Tailwind references and applied important modifiers.
- Updated transition.css to include Tailwind reference.
- Removed tailwind.config.cjs as part of the cleanup.

src/styles/markdown.css

@@ -1,3 +1,5 @@
+@reference "./main.css";
+
 .custom-md {
     h1 {
         @apply text-3xl;
@@ -5,16 +7,16 @@
 
     h1, h2, h3, h4, h5, h6 {
         .anchor {
-            @apply transition -m-0.5 ml-[0.2ch] p-0.5 select-none opacity-0 no-underline !important;
+            @apply transition -m-0.5! ml-[0.2ch]! p-0.5! select-none! opacity-0! no-underline!;
 
             .anchor-icon {
-                @apply mx-[0.45ch] !important;
+                @apply mx-[0.45ch]!;
             }
         }
 
         &:hover {
             .anchor {
-                @apply opacity-100 !important;
+                @apply opacity-100!;
             }
         }
     }