Sliding conditional formatting

Hi everyone,
I am currently stuck in Excel with the conditional formatting. I would like to apply a color to a cell in column A, row 1 based on a formula referring to the value of another cell in the same row 1 but in a different column (for example B). Easy. But then, I would like to extend this formatting to all the cell of the column A, applying formatting based on the content of the reference cell in column B and in the same row (not the initial one). for instance I want to format
A1 based on B1
A2 based on B2
A3 based on B3
...
I keep trying but struggle with it. Excel keeps using my very first reference B1 as reference for all. I tried the copy/past function, the format painter, the extension, but nothing is working... I also tried with the $ to use the referential function, but did not manage either...

Can anyone help me?
Thanks so much!
Mathieu