graphviz: make the diagrams' background transparent by default

No need to set a background color, is there?

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

assets/js/application.js

@@ -789,6 +789,9 @@ var Graphviz = {
       if (!vizInstance) vizInstance = await Viz.instance()
       const options = {
         format: "svg",
+        graphAttributes: {
+          bgcolor: "transparent",
+        },
       }
       const svg = vizInstance.renderString(x.innerText, options)
       const img = document.createElement('img')