fix: make heading anchors in article visible on mobile

Author: satnaing

src/layouts/PostDetails.astro

@@ -211,7 +211,7 @@ const nextPost =
       heading.classList.add("group");
       const link = document.createElement("a");
       link.className =
-        "heading-link ms-2 opacity-0 group-hover:opacity-100 focus:opacity-100";
+        "heading-link ms-2 no-underline opacity-75 md:opacity-0 md:group-hover:opacity-100 md:focus:opacity-100";
       link.href = "#" + heading.id;
 
       const span = document.createElement("span");