It’s currently not possible to add a border style via the CSS box on a block element (and perhaps other elements – haven’t checked).
CSS Box:
root {border: 5px solid red;}
CSS Output:
Any time you declare a border in CSS, its color is overridden by var(–bricks-border-color).
cmstew
2
This is related to a previously reported bug.
timmse
3
Hey Kevin,
Yep, it’s a duplicate 
I’ll close this thread.