DOCS: how to create an inline footer (#636)

Co-authored-by: Chris Holdgraf <[email protected]>

docs/user_guide/customizing.rst

@@ -143,6 +143,27 @@ For a complete list of the theme variables that you may override, see the
 .. literalinclude:: ../../src/pydata_sphinx_theme/theme/pydata_sphinx_theme/static/styles/theme.css
   :language: CSS
 
+Change footer display
+=====================
+
+Each footer element is wrapped in a ``<div>`` with a ``footer-item`` class, allowing you to style the structure of these items with custom CSS.
+
+For example, by default the footer items are displayed as blocks that stack vertically.
+To change this behavior so that they stack **horizontally**, add a rule like the following in your custom ``.css`` file.
+
+.. code-block:: css
+
+   // Make each footer item in-line so they stack horizontally instead of vertically
+   .footer-item {
+     display: inline-block;
+   }
+
+   // Add a separating border line for all but the last item
+   .footer-item:not(:last-child) {
+     border-right: 1px solid var(--pst-color-text-base);
+     margin-right: .5em;
+     padding-right: .5em;
+   }
 
 Replacing/Removing Fonts
 ========================