Thanks, Carra!
Regarding your question – initially the theme only contained icons of most popular social networks, but I am constantly working on expanding the choice. Since Foursquare has not been added yet, I’ve created a custom one for you; you can download it from our file repository: https://satoristudio.net/files/foursquare.png. In order for it to be displayed by the Social Media Widget, upload the image into the following folder: wp-content/themes/Fuji/includes/social-media-widget/images/fuji/32/ – or you are free to use it anywhere else on the website. Hope you like the icon, if so, I will include it in the next theme update :)
If you need other social icons that are not there yet, of custom-sized icons, do not hesitate to let me know!
Best,
Andrew.