kableExtra-2列的Collapse_rows（）对齐

Question

我正在使用KableExtra包来显示表格。我需要通过折叠行来显示数据框，还需要更改网格线的颜色。

使用的数据帧如下：

marksDF <- data.frame(
  Staff = c("Henry","Henry","Clay","Clay","Clay","Clay","Clay","David","Jensen","Jensen","Jensen","Alex","Alex","Alex","Alex","Alex","Alex","Alex"),
  Grade = c("9","10","11","11","12","12","8","9","9","9","9","9","9","9","9","9","10","11"),
  Term1 = c("0","0","4","3","1","3","0","2","0","40","0","0","10","3","3","0","5","2"),
  stringsAsFactors = FALSE
)

用于以表格格式显示数据框的代码为：

kable(marksDF, "html", booktabs = T, align = rep('c',2)) %>%
  kable_styling(latex_options = "striped", stripe_color = "red") %>%
  kableExtra::kable_styling(full_width = T) %>%
  column_spec(1)%>%
  collapse_rows(columns = 1:2) %>%
  row_spec(1:2, align = "c", color = 'black')

获得的输出是：

期望的产出是每位员工的等级。但是，对于David，Jensen，Alex的员工来说，我正在升入9年级。

如何使用kableExtra软件包实现这一目标？