### Summary Mermaid diagrams aren't rendered correctly in the iframe box generated by previews inside the rich text editor. ### Steps to reproduce - Select rich text editor - Select more options -\> Mermaid Diagram - Select preview icon ### What is the current _bug_ behavior? The iframe generated when previewing mermaid diagrams inside the rich text editor is empty. {width="447" height="187"} ### What is the expected _correct_ behavior? The preview renders a preview of the diagram while syntax is correct. ### Output of checks <!--If you are reporting a bug on GitLab.com, uncomment below--> This bug happens on GitLab.com <!--and uncomment below if you have /label privileges--> <!--/label ~"reproduced on GitLab.com"--> <!--or follow up with an issue comment of `@gitlab-bot label ~"reproduced on GitLab.com"` if you do not--> ### Possible fixes <!--If you can, link to the line of code that might be responsible for the problem.-->