fix(docs): suppress spurious vertical scrollbar on equations (#1162)

MathJax v4 (Sphinx 9) display equations can inherit overflow handling from pydata-sphinx-theme that introduces a spurious vertical scrollbar. Match the theme selector, preserve horizontal scrolling for wide equations, and suppress vertical overflow.

Signed-off-by: Joao Morais <jmoraispk@gmail.com>

Author: jmoraispk

doc/source/_static/custom.css

@@ -109,6 +109,15 @@ div.citation > p.cite-backrefs {
     margin-bottom: 0.3em !important;
 }
 
+/* MathJax v4 (Sphinx 9): the pydata theme sets `overflow: auto` on
+   `div.math mjx-container`, which adds a spurious vertical scrollbar to every
+   display equation. Match that selector to keep horizontal scroll for wide
+   equations while suppressing the vertical scrollbar. */
+div.math mjx-container {
+    overflow-x: auto;
+    overflow-y: hidden;
+}
+
 /* Rubric headings (Note, Example, Attributes, Methods, etc.): line below, consistent style */
 p.rubric {
     border-bottom: 1px solid var(--pst-color-border);