Whenever I'm testing my custom CSS out I find myself refreshing whatever random search result page I have open at the time. This likely costs Kagi money and would use up my searches if I was on a starter plan. Additionally not every search shows every UI element I might want to test (e.g. widgets, info sidebar).
Make a dummy search result page that applies a user's custom CSS. This dummy page should have all the elements one might see on a real search result, such as inline image results, inline video results, an example widget, a right-hand-side info box, etc.