pub(crate) fn get_popup_err_elem() -> Element {
        let document = web_sys::window().unwrap().document().unwrap();
        // If we can't get the error container, it's logical to panic
        document.get_element_by_id("__perseus_popup_error").unwrap()
    }
Gets the element for popup errors (used in both full startup and
critical failures).

This is created on the engine-side to avoid hydration issues.
packages/perseus/src/reactor/start.rs