diff --git a/docs/conf.py b/docs/conf.py
index 0b9ba7a4..4b95b57f 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -40,7 +40,10 @@
     "smartquotes",
     "deflist",
 ]
-mermaid_init_js = "mermaid.initialize({startOnLoad:true,theme:'neutral'});"
+mermaid_init_js = (
+    "mermaid.initialize({startOnLoad:true,"
+    "theme:document.documentElement.dataset.theme==='dark'?'dark':'neutral'});"
+)
 
 ogp_image = "_static/structlog_logo.png"