Fix broken math link icon

This likely was indirectly broken with da86e4d

This commit addes our standard headerlink icon styles to math links aswell, before they had no styling.

Fixes #1189

Author: Blendify

sphinx_rtd_theme/static/css/theme.css

@@ -206,7 +206,7 @@
     @extend h2
 
   // This is the #href that shows up on hover. Sphinx's is terrible so I hack it away.
-  h1, h2, h3, h4, h5, h6, dl dt, p.caption, table > caption, .code-block-caption
+  h1, h2, h3, h4, h5, h6, dl dt, p.caption, table > caption, .code-block-caption, .eqno
     .headerlink
       opacity: 0
       font-size: 14px