Sandbox all outputs in iFrame (#624)

src/Utils/StyleUtils.ts

@@ -0,0 +1,23 @@
+// Adapted from https://gist.github.com/davidgilbertson/ed3c8bb8569bc64b094b87aa88bed5fa
+export function copyStyles(sourceDoc: Document, targetDoc: Document): void {
+  Array.from(sourceDoc.styleSheets).forEach((styleSheet) => {
+    if (styleSheet.href) {
+      // for <link> elements loading CSS from a URL
+      const newLinkEl = sourceDoc.createElement("link");
+
+      newLinkEl.rel = "stylesheet";
+      newLinkEl.href = styleSheet.href;
+      targetDoc.head.appendChild(newLinkEl);
+    } else if (styleSheet.cssRules && styleSheet.cssRules.length > 0) {
+      // for <style> elements
+      const newStyleEl = sourceDoc.createElement("style");
+
+      Array.from(styleSheet.cssRules).forEach((cssRule) => {
+        // write the text of each rule into the body of the style element
+        newStyleEl.appendChild(sourceDoc.createTextNode(cssRule.cssText));
+      });
+
+      targetDoc.head.appendChild(newStyleEl);
+    }
+  });
+}