I need to design the R Shiny data table, using Java Script like that (like stairs on the DT bottom, which shows the prediction values - italic and gray).

I'm trying to use this function (From this question), but all my table is italic starting from 3rd column. How can I fix it? (suppose, that my for loop is incorrect)

  rowCallback <- function(rows){
c(
  "function(row, data, num){",
  sprintf("  var rows = [%s];", paste0(rows-1, collapse = ",")),
  "  for(let j=data.length; j >= 3; j--){",
  "    for(let i=j; i<data.length; i++){",
  "      $('td:eq('+i+')', row)",
  "        .css({'background-color': 'rgb(211,211,211)', 'font-style': 'italic', 'font-color': 'rgb(230,230,230)'});",
  "    }",
  "  }",
  "}"  
)

}