Feature: Make theme colors configurable.

_config.yml

@@ -67,6 +67,18 @@ disqus:
 # The year your website first ran.
 first_run: 2019
 
+
+# Prefer color scheme setting, available values:
+#
+#     dual   - Follow the system prefer color by default, and a toggle will display
+#              in the left bottom of Sidebar, which used for switch the theme between dark and light.
+#
+#     light  - Use the light color scheme
+#
+#     dark   - Use the dark color scheme
+#
+theme_mode: dual
+
 # boolean type, global switch for ToC in posts.
 toc: true