Issue 1957 Change theme palette scheme to slate

Author: sroopsai

mkdocs.yml

@@ -8,8 +8,9 @@ theme:
   custom_dir: 'theme'
   logo: ''
   palette:
-    primary: 'blue grey'
-    accent: 'indigo'
+    - scheme: 'slate'
+      primary: 'blue grey'
+      accent: 'indigo'
   language: en
   features:
     - navigation.tabs