update doc

Author: Yunnglin

docs/en/docs/_static/icon.svg

@@ -42,26 +42,26 @@ theme:
     - search.suggest
     - content.code.copy
     - content.code.annotate
+    - content.code.select
 
   palette:
     # Palette toggle for automatic mode
     - media: "(prefers-color-scheme)"
-      primary: indigo
       toggle:
         icon: material/brightness-auto
         name: Switch to light mode
 
     # Palette toggle for light mode
     - media: "(prefers-color-scheme: light)"
-      primary: indigo
+      primary: white
       scheme: default 
       toggle:
         icon: material/brightness-7
         name: Switch to dark mode
 
     # Palette toggle for dark mode
     - media: "(prefers-color-scheme: dark)"
-      primary: indigo
+      primary: black
       scheme: slate
       toggle:
         icon: material/brightness-4