use vs pygments scheme

Author: mmcky

lectures/_config.yml

@@ -72,7 +72,7 @@ sphinx:
     html_favicon: _static/lectures-favicon.ico
     html_theme: quantecon_book_theme
     html_static_path: ['_static']
-    pygments_style: colorful
+    pygments_style: vs
     html_theme_options:
       qetheme_code_style: False
       authors: