WordPress plugin
Plugin Version 4.0 and above
You can customize the feed by going to Facebook Feed > All Feeds > select Edit for the relevant feed. Here, you will see all the customization options for the feed and a preview of it on the right-hand side. You can navigate the Customize and Settings menu and the feed will be updated to view your changes. When finished, click Save in the top right-hand corner.
If you need further customization than the built-in options allow then you can add your own CSS to your preferred custom CSS location or stylesheet. One option is the default additional CSS location found at WordPress Dashboard > Appearance > Customize > Additional CSS
Below Plugin Version 4.0
You can customize the feed by setting the options on the Customize page, which can be found under the Facebook Feed menu in your left-hand WordPress admin menu. If you need even deeper customization than the built in options allow then you can add your own CSS to the plugin in the Custom CSS section under the Misc tab.
You can also override these styles for individual feeds by setting options within the shortcode. For example, you can change the height of a specific feed like so: [custom-facebook-feed height=500px]. See a full list of all shortcode options here.
Standalone version
You can customize the feed by settings the options in the fbfeed-settings.php file. If you need deeper customization then you can add your own custom CSS to your website’s stylesheet to completely customize the way the feed looks.
You can also override these styles for individual feeds by setting custom options which you can pass into the fbFeed() function. For example, you can change the height of a specific feed like so:
$custom = array(
'height' => '500px'
);
fbFeed($settings, $custom);