ace2_inner: Simplify document body selection

src/static/js/ace2_inner.js

@@ -3543,7 +3543,7 @@ function Ace2Inner(editorInfo, cssManagers) {
     // but as it's non-text type the line-height/margins might not be present and it
     // could be that this breaks a theme that has a different default line height..
     // So instead of using an integer here we get the value from the Editor CSS.
-    const innerdocbody = document.querySelector('#innerdocbody');
+    const innerdocbody = document.body;
     const innerdocbodyStyles = getComputedStyle(innerdocbody);
     const defaultLineHeight = parseInt(innerdocbodyStyles['line-height']);