So ...

We are going to use a handy plugin called Simple Custom CSS.

Here it is:

https://wordpress.org/plugins/simple-custom-css/

The plugin will allow you to add custom CSS styles that override plugin and theme default styles. What is really important: any new rule and style created with this plugin will render even if the theme is changed.

Other benefits:

• customizer Control
• useful Code Syntax highlighter
• code linting (error checking)
• no configuration needed
• virtually no impact on site performance
• thorough documentation

It's a very small plugin (204 KB), but let's see the usual speed tests ...

Here are my results before installing the plugin ...

... and the result after installing and activating the plugin:

No more comments needed ...

Now let's see how it works ...