Adjust color scheme for fluffy.guide (#2144)

Use the same scheme as for the nimbus.guide.
Two differences however:
- Set the dark scheme as default, considering the new nimbus.team
website also has dark as default.
- Remove the orange/amber for the light scheme, considering the
light version of nimbus.team has no more orange.

fluffy/docs/the_fluffy_book/docs/stylesheets/extra.css

@@ -0,0 +1,6 @@
+[data-md-color-scheme="slate"] {
+  --md-hue: 180;
+  --md-default-bg-color: hsla(var(--md-hue), 0%, 0%, 1);
+  --md-footer-bg-color: hsla(var(--md-hue), 0%, 0%, 1);
+  --md-footer-bg-color--dark: hsla(var(--md-hue), 0%, 0%, 1);
+}

fluffy/docs/the_fluffy_book/mkdocs.yml

@@ -14,9 +14,22 @@ theme:
     - navigation.top
     - content.tabs.link
   palette:
-    scheme: default
+    - scheme: slate
-    primary: orange
+      primary: black
-    accent: amber
+      accent: light blue
+      toggle:
+        icon: material/brightness-4
+        name: Switch to light mode
+    - scheme: default
+      primary: white
+      accent: light blue
+      toggle:
+        icon: material/brightness-7
+        name: Switch to dark mode
+
+
+extra_css:
+  - stylesheets/extra.css
 
 # Support urls previously used by mdbook
 use_directory_urls: false
@@ -26,7 +39,6 @@ docs_dir: docs
 
 markdown_extensions:
   - admonition
-  - meta
   - pymdownx.details
   - pymdownx.highlight:
       anchor_linenums: true