The opt_css() function

Use exibble to create a gt table and format the data in both columns. With opt_css(), insert CSS rulesets as as string and be sure to set the table ID explicitly (here as "one").

exibble |>
  dplyr::select(num, currency) |>
  gt(id = "one") |>
  fmt_currency(
    columns = currency,
    currency = "HKD"
  ) |>
  fmt_scientific(columns = num) |>
  opt_css(
    css = "
    #one .gt_table {
      background-color: skyblue;
    }
    #one .gt_row {
      padding: 20px 30px;
    }
    #one .gt_col_heading {
      text-align: center !important;
    }
    "
  )

num	currency
1.11 × 10−1	HK$49.95
2.22	HK$17.95
3.33 × 101	HK$1.39
4.44 × 102	HK$65,100.00
5.55 × 103	HK$1,325.81
NA	HK$13.26
7.77 × 105	NA
8.88 × 106	HK$0.44