The cells_grand_summary() function

Use countrypops to create a gt table. Add some styling to a grand summary cell with with tab_style() and cells_grand_summary().

countrypops |>
  dplyr::filter(country_name == "Spain", year < 1970) |>
  dplyr::select(-contains("country")) |>
  gt(rowname_col = "year") |>
  fmt_number(
    columns = population,
    decimals = 0
  ) |>
  grand_summary_rows(
    columns = population,
    fns = change ~ max(.) - min(.),
    fmt = ~ fmt_integer(.)
  ) |>
  tab_style(
    style = list(
      cell_text(style = "italic"),
      cell_fill(color = "lightblue")
    ),
    locations = cells_grand_summary(
      columns = population,
      rows = 1
    )
  )

	population
1960	30,455,000
1961	30,739,250
1962	31,023,366
1963	31,296,651
1964	31,609,195
1965	31,954,292
1966	32,283,194
1967	32,682,947
1968	33,113,134
1969	33,441,054
change	2,986,054