_content: show anchor links when hovering over article headers

Previously, users had to hover directly over the ¶ symbol to reveal the anchor link, making it difficult to discover its existence.

This change updates the CSS to also display the anchor link when hovering over the entire header text, improving usability.

Fixes golang/go#70827

Author: ysam12345

_content/css/styles.css

@@ -875,6 +875,10 @@ h1 + h2.subtitle {
 .Article a.Article-idLink {
   opacity: 0;
 }
+.Article h1:hover a.Article-idLink,
+.Article h2:hover a.Article-idLink,
+.Article h3:hover a.Article-idLink,
+.Article h4:hover a.Article-idLink,
 .Article a.Article-idLink:hover {
   opacity: 1;
   padding: 0.2rem;