docs: add dark mode toggle

mkdocs.yaml

@@ -1,6 +1,25 @@
 site_name: LAT_Alignment 
 site_url: https://simonsobs.github.io/LAT_Alignment/
-theme: material 
+theme: 
+  name: material 
+  palette:
+    # Palette toggle for automatic mode
+    - media: "(prefers-color-scheme)"
+      toggle:
+        icon: material/brightness-auto
+        name: Switch to light mode
+    # Palette toggle for light mode
+    - media: "(prefers-color-scheme: light)"
+      scheme: default 
+      toggle:
+        icon: material/brightness-7
+        name: Switch to dark mode
+    # Palette toggle for dark mode
+    - media: "(prefers-color-scheme: dark)"
+      scheme: slate
+      toggle:
+        icon: material/brightness-4
+        name: Switch to system preference
 plugins:
   - search
   - mkdocs-homepage-copier