Alternate approach

source/_static/customize.css

@@ -1,8 +1,13 @@
 /**
 Make max width wider on wide displays
 */
-@import url("theme.css")
 
-.wy-nav-content {
-  max-width: 90% !important;
+.wy-table-responsive table td, .wy-table-responsive table th {
+    /* !important prevents the common CSS stylesheets from
+       overriding this as on RTD they are loaded after this stylesheet */
+    white-space: normal !important;
+}
+
+.wy-table-responsive {
+    overflow: visible !important;
 }

source/conf.py

@@ -112,7 +112,9 @@
 import sphinx_rtd_theme
 html_theme = "sphinx_rtd_theme"
 html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
-html_style = 'css/customize.css'
+
+# See the setup method at end of conf.py
+#html_style = 'css/customize.css'
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
@@ -296,3 +298,7 @@
 
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {'API':('https://releases.dataone.org/online/api-documentation-v2.0', None)}
+
+
+def setup(app):
+  app.add_stylesheet('css/customize.css')