Sometimes it will be necessary for you to add some custom CSS to your site to make it exactly how you want.
The easiest way is to install Simple CSS. This plugin allows you to enter CSS into a nice editor in your Dashboard without having to create any files or do anything else complicated.
Another perk to this plugin is the CSS meta box you can find on each individual page. This allows you to add CSS that only applies to that one page, which can be incredibly useful.
To install it, simply go to Plugins > Add New in your Dashboard and search for Simple CSS.
In WordPress 4.7, WordPress added a core way to add CSS to your site inside the Customizer which you can find in Customize > Additional CSS.
It should be noted that the CSS added in this area is theme-specific, so if you switch themes, you’ll lose your CSS.
It also doesn’t have the individual page meta box for page specific CSS.
Using a Child Theme
Of course, if you’re already using a child theme, you can use the style.css file.
If you’re only adding CSS to your website, a child theme is probably overdoing it a bit – you’re better off using one of the methods above.