Pot funding amount - make it obvious about custom amounts

Many people here (including my wife) expressed surprise when told they could easily transfer any amount to/from their pots and not just the ‘+/- £xx’ amounts by pressing the digits and then entering the amount they wanted to transfer.

To improve usability and friction on this front, would it be possible to have a border around the digits in the same colour as the +/- to try and make it more obvious it can be interacted with and modified? [Wife’s idea!]