Need help changing part of my template

I’m using i3theme-1-7-classic template for my wordpress.

I badly need help changing part of my template. There’s one bit that’s been troubling me for ages now and it’s driving me mad lol!

https://www.forbescreatives.com/blog

If you look at the link above you will see these bright white thick borders around various parts of my template….How do I change the colour of these. I’ve altered every part of my style sheet and still can’t find the code to change the color of the white border.

Any help will be appreciated.

Thanks.