I think the issue here is specificity, a CSS subject that is confusing. I don’t claim to understand it completely, but…
I think what is happening is that you are giving image a class of
img which is a Bootstrap class. Since that has a high specificity, it is difficult to override. But since you want to manually control the borders, I would remove this class entirely.
But now I see that you are editing your pen as I am writing this, so you seem to have figured it out. Putting it under the
warren-photo class has a higher specificity. I think it is
id > class > element. And it is cumulative. And Bootstrap classes have a high specificity.
It is a confusing subject, but whenever I can’t control something that I know I should be able to, specificity is often the cause.
I would also suggest that you not worry too much about pixel perfect CSS for your first project. CSS is a complex subject and FCC only gives you the bare basics. I would take advantage of the Bootstrap styling and let that be good enough. You can go back later and study for a year and become a CSS wizard.