Blog Post Header

Site URL: https://myanmarhope.org/myhopeblog/follow-our-march-trip

How do I add a header image to my blog posts? Right now it's plain white, and that is very different from the rest of the pages on my site. I've tried everything I can think of, but I don't see any option to add a header to the actual blog posts pages.

Add to Home > Design > Custom CSS

.collection-type-blog.view-item header.Header.Header--bottom {
    background-image: url(https://beaverhero.com/wp-content/uploads/2019/12/squarespace-2-languages-sites.png);
    background-size: cover;
    background-repeat: no-repeat;
    background-position: center center;
}