Centring The Shortcode/Feed

Hey there,

love the plugin, thanks very much!

Myself and I can see a few others here, are wondering how to centre the shortcode. I cannot figure out how to make it centre align. I’ve used it on several clients websites and it always floats left! I’m a coding novice, but couldn’t find the css for the plugin to try edit that either. Any help would be really appreciated!

Here are two examples using the same theme with the plugin:
http://www.ramcat.com.au/
http://g3fitness.com.au/

https://wordpress.org/plugins/simple-instagram/