Additional CSS

Although the REI Website theme comes with plenty of options to style and customize your site, you may wish to add some of your own custom CSS to style specific elements of your website. This is only recommended if you have HTML and CSS experience.

Adding Additional CSS

Go to Appearance → Customize
Click Additional CSS in the Customize Control on the right.
You will be presented with a custom code box where you can paste in code or type in your custom styles. Make sure to write code without the <style>...</style> tag.
When you're finished, click Publish.

NOTE WordPress have provided a guide to help you with what you need to know about adding custom CSS to your theme. You can read this article here.