Integrate with mermaid-js

_includes/mermaid.html

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+<!--
+  mermaid-js loader
+-->
+<script src="https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.min.js"></script>
+<script>
+
+  let initTheme = "default";
+
+  if ($("html[mode=dark]").length > 0
+    || ($("html[mode]").length == 0
+      && window.matchMedia("(prefers-color-scheme: dark)").matches ) ) {
+    initTheme = "dark";
+  }
+
+  let mermaidConf = {
+    theme: initTheme  /* <default|dark|forest|neutral> */
+  };
+
+  /* Markdown converts to HTML */
+  $("pre").has("code.language-mermaid").each(function() {
+    let svgCode = $(this).children().html();
+    $(this).addClass("unloaded");
+    $(this).after(`<div class=\"mermaid\">${svgCode}</div>`);
+  });
+
+  mermaid.initialize(mermaidConf);
+
+</script>