By default your Facebook feed should inherit the font from your website. If this isn’t the case then it’s possible that something in the theme is preventing this from happening. An issue that we’ve run into before is that <code> tags are added into the plugin HTML by either the theme, another plugin, or perhaps even the shortcode being wrapped in code tags in your page editor. To fix this;
1) First – go to your page editor, click on the ‘Text’ tab in the top right of the editor box, and check whether the shortcode is being wrapped in <code>, like so: <code>[custom-facebook-feed]</code>. If it is, then remove them.
2) If this doesn’t solve the problem then try adding the following to your preferred custom CSS location or stylesheet. One option is the default additional CSS location found at WordPress Dashboard > Appearance > Customize > Additional CSS.
#cff code { font-family: sans-serif; }
You can replace the font-family with whatever font your theme is using.
Note: you can also set custom Google fonts on your feed by following the directions in this FAQ
