Conditional Formatting with icon sets

Can you apply cf to a single cell, or do you need a range of cells?
My rules work fine with highlighting the cell [red, yellow, green], but the same rule will not work with an icon set for the same data. [single cell]. I'm not a very advanced user. I downloaded an example of cf, but it didn't work after I changed the values.

The same happened in my data: it worked correctly the first time, but when I adjusted the data, it did not work a second time. I'm trying to create sort of a dashboard for some standards [mostly percentages], but the input data may change each month.

Thank you.