So ...

It's extremely simple ... Upon activation you'll notice a new "Custom CSS" menu item under "Appearance":

And again, all you have to do is to write or paste your custom CSS code ...

BUT! This awesome plugin allows you to implement and store your custom CSS independently from your theme!

In other words, you can easily switch and/or update your themes without losing the custom CSS. And you can easily edit the plugin's Simple Custom CSS code even in your customizer:

Also, this method can be very useful for users who are not using WordPress 4.7 or later versions of WordPress ...

And that's it my friends! If you have any comments, further questions or update requests please don't hesitate to react! Like, comment and share!

Other related tutorials may want to see:

How to choose the perfect theme for your website

Why and how to test your Wordpress website in different browsers

Why and how to export and import your theme customizer settings in Wordpress

How to find which theme files to edit when you are customizing your theme

The easiest and safest way to manage the automatic Wordpress updates

And don't forget, you can easily come back to this tutorial whenever you want.

All you need to do is to bookmark the categorized, daily updated register of my blogs and training materials. Here it is:

Posts and training by smartketeer

Thanks for your time!