Detect default dark themes for mermaid diagrams

Author: detrumi

book/mermaid-init.js

@@ -1 +1,4 @@
-mermaid.initialize({startOnLoad:true});
+mermaid.initialize({
+    startOnLoad: true,
+    theme: ['coal', 'navy', 'ayu'].includes(theme) ? 'dark' : 'default',
+});