New source found from dndbeyond.com

ddb_main/node_modules/@mui/styled-engine/index.js

@@ -1,5 +1,5 @@
 /**
- * @mui/styled-engine v5.15.14
+ * @mui/styled-engine v5.18.0
  *
  * @license MIT
  * This source code is licensed under the MIT license found in the
@@ -9,6 +9,7 @@
 
 /* eslint-disable no-underscore-dangle */
 import emStyled from '@emotion/styled';
+import { serializeStyles as emSerializeStyles } from '@emotion/serialize';
 export default function styled(tag, options) {
   const stylesFactory = emStyled(tag, options);
   if (process.env.NODE_ENV !== 'production') {
@@ -33,6 +34,14 @@ export const internal_processStyles = (tag, processor) => {
     tag.__emotion_styles = processor(tag.__emotion_styles);
   }
 };
+
+// Emotion only accepts an array, but we want to avoid allocations
+const wrapper = [];
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export function internal_serializeStyles(styles) {
+  wrapper[0] = styles;
+  return emSerializeStyles(wrapper);
+}
 export { ThemeContext, keyframes, css } from '@emotion/react';
 export { default as StyledEngineProvider } from './StyledEngineProvider';
 export { default as GlobalStyles } from './GlobalStyles';