first commit

common/resources/client/core/root-el.ts

@@ -0,0 +1,14 @@
+export let rootEl = (
+  typeof document !== 'undefined'
+    ? document.getElementById('root') ?? document.body
+    : undefined
+) as HTMLElement;
+
+export let themeEl = (
+  typeof document !== 'undefined' ? document.documentElement : undefined
+) as HTMLElement;
+
+export function setRootEl(el: HTMLElement) {
+  rootEl = el;
+  themeEl = el;
+}