Google Sheets Conditional formatting of multiple cells with different colors

I study for a big exam and want to set priorities with the help of conditional formatting. For example, if C90, C91, C92 are blank, the color would be white; if C90, C91 are blank but C92 is not blank, the color would be yellow; if C90, but C91 and C92 are not virgin, the color would be red; and if all three are not empty the color would be red. I want to apply this to all headers. I hope it makes sense! Thanks in advance!