The below code create a dataframe with variable `test1_score` and `test2_score`. I need to change background of `test2_score` if it is more than `test1_score`. 

Below is the code to create the create the dataframe:

```
df <- data.frame(
  id = 1:10,
  name = c("Bob", "Ashley", "James", "David", "Jenny", 
           "Hans", "Leo", "John", "Emily", "Lee"), 
  age = c(28, 27, 30, 28, 29, 29, 27, 27, 31, 30),
  grade = c("C", "A", "A", "C", "B", "B", "B", "A", "C", "C"),
  test1_score = c(8.9, 9.5, 9.6, 8.9, 9.1, 9.3, 9.3, 9.9, 8.5, 8.6),
  test2_score = c(9.1, 9.1, 9.2, 9.1, 8.9, 8.5, 9.2, 9.3, 9.1, 8.8),
  final_score = c(9, 9.3, 9.4, 9, 9, 8.9, 9.25, 9.6, 8.8, 8.7),
  registered = c(TRUE, FALSE, TRUE, FALSE, TRUE, TRUE, TRUE, FALSE, FALSE, FALSE),
  stringsAsFactors = FALSE)

```

I am using `DT` for formating tables.
Used the below code but getting blank table as output.

```
datatable(df) %>%
  DT::formatStyle(columns = "test2_score", valueColumns = "test1_score", 
  backgroundColor = styleInterval("test1_score", c('gray', 'yellow')))

```