Unique Header #page-sub-header css on Post page

Hi,
I’m using the plugin Unique Headers with WP Bootstrap Starter and it works on every page, except the main blog posts page. The posts themselves are fine, just the page with Recent Posts isn’t working correctly, and I’m pulling my hair out to know why.

I’ve tried
.blog #page-sub-header {
*css code*
}
but that hasn’t worked (with and without the .blog part).

Any help would be greatly appreciated. Thank you in advance!

The page I need help with: [log in to see the link]