Mac - Custom Crop - How please?

In Windows I can enter a custom crop either by entering a ratio (1.5) or by entering the size or a representation of the size (1920x1080 or 16x9). This seems to be missing in the mac version. When I click the crop icon at the top, PL6 goes into crop mode but the drop-down (at the bottom) does not contain custom. It contains original, unconstrained, a load of presets and at the bottom, the option to clear custom - but no custom. The crop numbers just along the bottom are greyed out and I cannot click to enter different numbers. What am I doing wrong please?

Clive

Just type into the text box that shows the current ratio

@Joanna - Thank you for your response.

If you are referring to the px dimensions on the line immediately below the image (with Crop icon on left end and Close on right end) then mine are greyed-out - I cannot click in the two fields (between the Show Grid item and the two rotate left/right icons).

Clive

Just tap on the selected ratio below the popup list, delete whta’s in it and start typing

@Joanna - Ah-ha, that one. You know where I was trying to enter! Now it works - thank you.

Clive