A caching plugin is a WordPress plugin that saves pre-built versions of your pages and serves them to visitors instead of generating each page from scratch on every request. Common examples include WP Rocket, W3 Total Cache, WP Super Cache, and LiteSpeed Cache. Caching makes sites load faster, but it introduces a specific problem when you're trying to debug visual issues.
When you make a CSS change and it doesn't appear on the page even after a browser refresh, the caching plugin may be serving a stored version of the page that was built before your change. Your stylesheet has the new rule. The cached page is delivering the old one. A hard browser refresh (Ctrl+Shift+R or Cmd+Shift+R) bypasses the browser's local cache but doesn't bypass the server-side page cache that the plugin maintains.
To see your changes: clear the caching plugin's cache from its settings page in your WordPress admin, then do a hard refresh in the browser. If Loupely Lens produces a diagnosis and you paste in the override prescription but still don't see a change after saving, clearing the caching plugin is the first thing to check before assuming the fix didn't take effect.