switch to material theme

Needed for tabbed code blocks.

docs/library/Getting-Started.md

@@ -30,7 +30,6 @@ under `/usr/local/share/nominatim/lib-python`. If you have installed
 Nominatim under a different prefix, adapt the `/usr/local/` part accordingly.
 You can also point the PYTHONPATH to the Nominatim source code.
 
-
 ### A simple search example
 
 To query the Nominatim database you need to first set up a connection. This

docs/mkdocs.yml

@@ -1,5 +1,8 @@
 site_name: Nominatim Documentation
-theme: readthedocs
+theme:
+  name: material
+  features:
+    - navigation.tabs
 docs_dir: ${CMAKE_CURRENT_BINARY_DIR}
 site_url: https://nominatim.org
 repo_url: https://github.com/openstreetmap/Nominatim
@@ -58,7 +61,8 @@ markdown_extensions:
     - codehilite
     - admonition
     - pymdownx.superfences
-    - pymdownx.tabbed
+    - pymdownx.tabbed:
+        alternate_style: true
     - def_list
     - toc:
         permalink: 