Assign gfm-mermaid class to mermaid diagrams and add appropriate CSS to ensure...

Assign gfm-mermaid class to mermaid diagrams and add appropriate CSS to ensure the width of the rendered SVG doesn't exceed that of the browser.

app/assets/javascripts/behaviors/markdown/render_mermaid.js

@@ -82,7 +82,7 @@ function renderMermaidEl(el) {
       return;
     }
 
-    svg.classList.add('mermaid');
+    svg.classList.add('mermaid', 'mw-100');
 
     // pre > code > svg
     svg.closest('pre').replaceWith(svg);

ee/changelogs/unreleased/37282-mermaid-diagram-scaling-fix.yml

+---
+title: Force mermaid diagrams to be scaled to fit within browser window when used in markdown
+merge_request: 25016
+author: Christopher Stryker
+type: fixed