Conditional format formula for highlighting a column that is blank

Good morning all

My first post, thus far all my previous questions have been answered by searching the forum.

I have a spreadsheet that has 200 rows and 275 columns.
As you will see in the example it is to do with comparing files with their functions. If a file uses a certain function then there is a "X" in the cell.
What I would like to do is highlight the columns that are completely blank (We are trying to reduce the functions in the system so would like to see which ones are not being used at all)
In my example the outcome would be that Column C, D, F, G, H, I, J, and K would be highlighted as there is no data inside any of the cells.

Thank you for any upcoming help in this.