Update md headlines. (#1105)

<!--
![image](https://github.com/user-attachments/assets/9243ae97-c17a-4927-930c-ed2fc1e65f3b)
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![image](https://github.com/user-attachments/assets/df42570a-bc76-4471-b368-020b477877e3)

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: nikoshell

astro.config.mjs

@@ -48,10 +48,7 @@ export default defineConfig({
       [
         rehypeAutolinkHeadings,
         {
-          behavior: "append",
-          content() {
-            return [h("span.heading-link", "#")];
-          },
+          behavior: "wrap",
         },
       ],
     ],

src/styles/global.css

@@ -54,6 +54,15 @@ body {
   text-decoration: none !important;
 }
 
+.prose :is(h1, h2, h3, h4, h5, h6) a:hover {
+  text-decoration: underline !important;
+}
+
+.prose :is(h1, h2, h3, h4, h5, h6) a:focus {
+  outline: 4px solid #0073e6;
+  outline-offset: 5px;
+}
+
 ul.milestone-done li {
   position: relative;
   list-style: none;