Help with borders

Hi everyone, looking for some help here.

I’m customizing an installation:

https://www.metrixfocus.com/blog/

And I’m trying to get the grey borders on the left and sides to be a thin dot border to match the rest of the site. I’ve gone over the CSS files a few times and just can’t seem to find where this is located. I’m using 2.7 and working off of the default theme. Any tips would be greatly appreciated – thank you!