Poul,
Don't know what you did with editing the shipping theme that didn't work, but the custom.css you're using won't do what you want.
What you're showing doesn't change the behavior of Bruce's css. You need to include something for that selector that overrides what's in the original css.
Something like this, for example, should work in your custom.css:
@media (max-width: 1024px) { /*for small screens */
.nt-browse-row-header{
display:flex!important;
}
}