Make sure the text box starts out in sync.

src/Editor.tsx

@@ -1,4 +1,4 @@
-import React, { ReactNode, useMemo, useRef, useState } from "react";
+import React, { ReactNode, useEffect, useMemo, useRef, useState } from "react";
 import "./Editor.css";
 import { Highlight } from "./highlight";
 import { buildShadow } from "./shadow";
@@ -72,6 +72,11 @@ function Editor({ defaultValue = default_org_source }) {
     }
   }
 
+  useEffect(() => {
+    // Make sure the text area and shadow div start out in sync.
+    onTextAreaScroll();
+  }, []);
+
   return (
     <div className="Editor">
       <div className="Editor-textwrapper">