Fix #3942: html: table is not aligned to center even if `:align: center`

CHANGES

@@ -30,6 +30,7 @@ Bugs fixed
 * #3953: Do not raise warning when there is a working intersphinx inventory
 * #4487: math: ValueError is raised on parallel build. Thanks to jschueller.
 * #2372: autosummary: invalid signatures are shown for type annotated functions
+* #3942: html: table is not aligned to center even if ``:align: center``
 
 Testing
 --------

sphinx/themes/basic/static/basic.css_t

@@ -332,6 +332,11 @@ table.docutils {
     border-collapse: collapse;
 }
 
+table.align-center {
+    margin-left: auto;
+    margin-right: auto;
+}
+
 table caption span.caption-number {
     font-style: italic;
 }