Reduce font size in schema reference, make 4 columns

PiperOrigin-RevId: 556719771
Change-Id: Ie1cf7ef02dab7fdd1eed40ce77ddaa71918a9754

doc/XMLreference.rst

@@ -28,6 +28,8 @@ through elements and attributes. Text content in elements is not used; if presen
    **R**  optional element, can appear many times recursively
    ====== ===================================================
 
+   .. cssclass:: schema-small
+
    .. include:: XMLschema.rst
 
 

doc/css/theme_overrides.css

@@ -18,6 +18,10 @@ body {
   color: var(--body-color);
 }
 
+.schema-small {
+  font-size: 93%;
+}
+
 .sidebar-brand-text {
   display: none;
 }
@@ -192,7 +196,7 @@ table.mjcf-attributes tbody tr td,
 table.mjcf-attributes tbody tr:nth-child(2n-1) td {
   border-style: none;
   padding: 0px 0px 0px 0px;
-  width: 33%;
+  width: 25%;
 }
 
 table.mjcf-attributes tbody tr td p {