Default dimensions for textarea custom field

I have created a custom field for visitors to leave a comment on the products page. It is of type Textarea. However the initial size on the box is small and customers will always have to drag it out to display the full contents of the Default Value. So can I change the default dimensions of the text area field?

Yes, you can change the number of rows and columns of the custom field in the options of the custom field.

And what about if I want the Label "Comments" to appear on top of the TeatArea and not to the left of it?

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There is no option for that.