Add syntax highlighting

internal/service/static/js/render.js

@@ -805,3 +805,22 @@ export class Renderer {
     );
   }
 }
+
+// Configure marked to use highlight.js for syntax highlighting.
+// marked v8+ removed the highlight option from setOptions; use the
+// marked-highlight extension instead.
+if (
+  typeof marked !== 'undefined' &&
+  typeof markedHighlight !== 'undefined' &&
+  typeof hljs !== 'undefined'
+) {
+  marked.use(
+    markedHighlight.markedHighlight({
+      langPrefix: 'hljs language-',
+      highlight(code, lang) {
+        const language = hljs.getLanguage(lang) ? lang : 'plaintext';
+        return hljs.highlight(code, { language }).value;
+      },
+    }),
+  );
+}