Hello @blueman,
The icon is displaying fine even in the browser as you can see in below screens shot when tested locally.
https://image.prntscr.com/image/6lXoeCHFQb2PZGQa-hn5Ew.png
Please make sure you have enabled Go to Top icon by going to Admin Panel > Appearance > Customize > Theme Options > Footer Options .
The feature to change the color of the icon is available within the theme . You just need to go to Admin panel > Appearance > Customize > Color Options > Go To top color Option and change the colors as per your wish .
Hope this helps.
Best Regards!!