Explanation
To know if a CSS file containing small changes was actually deployed to the org, one way that a developer can accomplish this is by right-clicking the CSS file and choosing Diff File Against Org. Diff File Against Orgis an option that allows the developer to compare a local file with its remote version in the org using Salesforce CLI commands. The developer can use Visual Studio Code to execute these commands by right-clicking on files or folders in the project and choosing from various diff options. Right-clicking the CSS file and choosing Diff File Against Org allows the developer to see the differences between the local CSS file and the remote CSS file in the org side by side in Visual Studio Code. This way, the developer can verify if their changes were deployed successfully or not. Clicking the Tools menu and selecting Diff Styles Against Org... is not a valid way to know if a CSS file was deployed to the org, as there is no such option in Visual Studio Code or Salesforce CLI. Right-clicking the folder for the component and choosing Diff Styles Against Org is not a valid way either, as there is no such option in Visual Studio Code or Salesforce CLI.
Right-clicking the folder for the component and choosing Diff Files Against Org is not a valid way either, as it will compare all the files in the folder, not just the CSS file, which may not be efficient or necessary.
Salesforce References: [Salesforce CLI Command Reference: force:source:diff], [Salesforce Developer Tools for Visual Studio Code]