How to add specific line to a gt table

This is a follow up question to this.

Background: I’m trying to mimic the table format used in the DCR journal.

In my gt table I only want 3 lines as shown here (my desired output):

To achieve this I use gt::opt_table_lines(extent = "none") to remove all lines, and add the 3 lines manually.

Here is my code (note there is no line under Primary Localisation):

library(gt)
library(gtsummary)

tbl_trial <- trial |>
  tbl_summary(by = trt, includ = c(age, grade)) |>
  add_p(pvalue_fun = label_style_pvalue(digits = 2)) |>
  add_overall() |>
  add_n() |>
  modify_header(label ~ "**Variable**") |>
  modify_spanning_header(c("stat_1", "stat_2") ~ "**Treatment Received**") |>
  modify_footnote_header("Median (IQR) or Frequency (%)", columns = all_stat_cols()) |>
  bold_labels() |> 
  modify_spanning_header(all_stat_cols() ~ "**Primary Localisation**") |> 
  as_gt() |> 
  # Removes all lines
  gt::opt_table_lines(extent = "none") 
  
  
tbl_trial |> 
 gt::tab_header(
    title = gt::md("TABLE 2. Tumor characteristics")
  ) |>
  
  gt::tab_style(
    style = gt::cell_text(align = "left", weight = "bold", color = "white"),
    locations = gt::cells_title(groups = "title")
  ) |>
 
   gt::tab_style(
    style = gt::cell_fill(color = "#0066b3"),
    locations = gt::cells_title(groups = "title")
  ) |>
# Line 1 
# Thin blue line under spanning header ("Primary Localisation")
  tab_options(column_labels.border.bottom.color = "#0066b3") |>
  gt::tab_style(
    style = cell_borders(
      sides = "bottom",
  color = "#0066b3",
      weight = px(1)
    ),
    locations = gt::cells_column_spanners()
  ) |>
# Line 2
# Bold blue line under column labels ("Characteristics")
gt::tab_style(
    style = gt::cell_borders(
      sides = "bottom",
      color = "#0066b3",
      weight = px(3)
    ),
    locations = gt::cells_column_labels()
) |> 
# Line 3
# Bold blue line at the bottom of the table
tab_style(
  style = cell_borders(
    sides = "bottom",
    color = "#0066b3",
    weight = px(3)
  ),
  locations = gt::cells_body(rows = nrow(tbl_trial[["_data"]]))
)

My question:

How can I add the line under Primary Localisation manually?

Simply add

|> opt_css(css = "
     .gt_column_spanner {
           border-bottom-style: solid !important;
           border-bottom-width: 3px !important;
     }")

_{as per my previous answer}