CSS not work after ajax replace
In some cases it can depend on how and where you have added your CSS to the page.

The best way to do it is using #attached on your field via hook_form_alter() or similar.

If your CSS is already on the page though it should work on new elements added with ajax.

One possible cause is that your CSS selectors are too specific and the ID/class used isn't matching properly with the markup added by the ajax.