theming – How to style Search API search block to look like the default?

I’m using Drupal 9.0.8 with W3CSS THEME FOR DRUPAL (8 & 9) ⚡️ and Search API & Search API Pages modules.
Having removed the core Search module I am now using the search block provided by the Search API Pages module. I would like to style this search block to look more like the one removed with the core module, with the inline search button and FontAwesome icons but I don’t know where to begin. I can’t even find the CSS that styled the original search block to crib it. Please can anyone point me in the right direction?