Conditional formatting a cell based on another cell


What I'm looking to achieve is a font in column A to be a colour (blue) if there is no text in column S, however, if there is text in column S then column A font turns black.

For example, if I type in cell A3, the colour is blue, and there is no text in S3. However, if i type anything (letters, numbers etc.) in cell S3, then A3 turns black. I'd also like to apply the rule for the rest of the columns in the table (ie. A4 and S4, A5 and S5 etc.)

I would assume it would be conditional formatting based on blank cells but I can't find a way of sourcing the data for a different cell.

Many thanks,