use customcss for viewing-outdate-docs message

conf.py

@@ -336,3 +336,6 @@ texinfo_documents = [
 intersphinx_mapping = {"cpython": ('https://docs.python.org/3/', None),
                        "bus_device": ('https://circuitpython.readthedocs.io/projects/busdevice/en/latest/', None),
                        "register": ('https://circuitpython.readthedocs.io/projects/register/en/latest/', None)}
+def setup(app):
+    app.add_stylesheet("customstyle.css")
+

docs/static/customstyle.css

@@ -10,6 +10,19 @@
 }
 
 
+/* custom CSS to sticky the ' viewing outdated version'
+   warning
+*/
+.document > .admonition {
+    position: sticky;
+    top: 0px;
+    background-color: salmon;
+    z-index: 2;
+}
+
+body {
+    overflow-x: unset!important;
+}
 
 /* override table width restrictions */
 @media screen and (min-width: 767px) {