One line with text on the left and on the right, and a rule: under the text for `bb_running_header()`, above it for `bb_page_footer()`. Both replace `{page}`, `{pages}` and `{<name>}` (from the page's `data`) when the page is exported, so one template serves every page.
Usage
bb_running_header(left, right = NULL, style = header_line_style())
bb_page_footer(left, right = NULL, style = footer_line_style())