To easily add custom CSS to your WordPress site, you can follow these steps:
Log in to your WordPress dashboard and go to Appearance > Customize.
In the Customizer, click on the Additional CSS option. This will open a text editor where you can add your custom CSS code.
Add your custom CSS code to the editor. For example, if you wanted to change the background color of your site, you could add the following code:
body {
background-color: #f1f1f1;
}
Preview your changes by clicking the Preview button in the Customizer. If you're happy with the changes, click the Save & Publish button to apply the changes to your live site.
Note that adding custom CSS using the Customizer will apply the changes globally to your entire site. If you want to apply the changes to a specific page or section of your site, you can use a plugin like Custom CSS and JavaScript or add the CSS directly to the relevant page or post using the page or post editor.
Also, be careful when adding custom CSS code, as an error in the code could break your site's appearance. It's a good idea to make a backup of your site before making any major changes, and to test your changes thoroughly before publishing them to your live site.