If you have ended up here, then there is a good chance we have instructed you to add some CSS to your themes style.css file in order to fix a styling issue.
Editing your themes style.css file is not strictly the only way to get some custom CSS into your site, you have a few options which we’ll go through below.
1. Editing your themes style.css file
This is probably the fastest way to get some custom CSS onto your site, but should only be used if you have created a child theme. If you have not created a child theme, and do not wish to make one, then take a look at option 2 or 3 instead.
Go to Appearance > Editor and select ‘style.css’ from the list of files on the right. This will load up the style.css file into the editor.
Right at the bottom of the file, on a new line, paste in the custom CSS and Save the file.
Remember to clear any WordPress cache plugins (W3 Total Cache, WP Super Cache etc), and clear your browser cache in order to see your changes.
2. Using your themes built in ‘Edit CSS’ option
Depending on your theme, you may have an ‘Edit CSS’ or ‘Custom CSS’ option built in (take a look under the ‘Appearance’ menu, or maybe in the Theme Settings). If you have this option then you should use it.
Paste in the custom CSS and Save.
3. Using the ‘Simple Custom CSS’ plugin
Install ‘Simple Custom CSS’ by going to Plugins > Add New, and searching for ‘Simple Custom CSS’.
After installation, go to Appearance > Edit CSS and paste in your custom CSS.
More information about this plugin can be found here: http://wordpress.org/plugins/simple-custom-css/